56040520-mine-surveying.pdf 544g1

Surveys

I.

The

root-mean

square

errors

Ma

of fl

direction angles of traverse sides incurred by the errors of angular measurements are determined by the formula:

= 45 Ma

= (mfl/c)J[Ji"!]

(4.17)

fl

is the distance between the plummets (here c = 75 m); Ry. are the projections onto the line 0 102 of 'the distances from the plumb line points 01 and O2 to the points of traverses run from the junction point to these plummets (here: Ry , Ry .and Ry ); p" = = 206265"; and n is the nfImber ofrJeasured angles between the approach point and junction point (here n = 2). The magnitudes of Ry. are taken from the survey plan; the s; sin2
where mfl is the rms error of angular measurements; Ry is the projection onto the line 0102 of the distances from each plummet to the points of the traverse section which connects the plummet with the side in question (including one point of that side). The values of Ry are determined on the survey plan (Table 4.3). Substituting the numerical values into formula (4.17), we obtain: for the first side of connection traverse (I-II):

M

"pVIl-VIlI

20J23650 115

=

27'

-102 x 6917

4 x 1010 x I x 10-6

752+

x 45

752

\I -+2 x

4.8.2.

102 =

25"

Estimating the Accuracy of Connection by Connecting Polygon

Suppose that a polygonometric traverse has been run through points I, II, III, IJ-: J-: n, nI, and nII (see Fig.4.10b). It is required to find the error of direction angles of the first, last, and middle side of the traverse

2. The root-mean square errors M~ of the direction angles of traverse sides incu;red by errors in linear measurements of side lengths are found by the formula: Ms = (J.1/c) p" j;;"Sj;;;-;p-;

(4.18)

where Si are the lengths of traverse sides and
4.8.

Horizontal

Connection

Survey

via Vertical

Shafts

53

Table 4.3

for the first side of traverse (I-II):

traverse (Fig. 4.11 ): Side 01-1 sisin2
I-II II-III 52 8 VII-VIII 5

III-IV 0

VIII-O2 0

M. = 0.001/115 x 2 x 105 Jill

IV-V 0

[sisin2
=

JM;.

+

M;

(4.19)

..

Fig. 4.11 Double projection connecting polygon

for the last side (VII-VIII): M ~VII-VIII = V /272 ~I + T 202 ~v = 34" and for the middle side (IV -V):

= 20"

3. The root-mean square errors of the direction angles of traverse sides relative to the p1umb-connecting line 0102 are calculated by the formula: M«

M ~1-II= V /362 :Ju + T 202 ~v = 42"

of side length of

M ~IV-V= V /122 l~ + T 202 ~v = 23" On the basis of these preliminary calculations of errors, the work superviser (chief surveyor) chooses the techniques and instruments which can ensure the specified accuracy of mine surveying. The entire complex of angular and linear observations on the surface and in the mine is carried out before hanging the plummets into the shafts. Mter hanging the plummets, their points are connected by measuring the angles at the first and last points of the connecting polygon and the distances from these points to the plummets. The coordinates x, y of the plummets O 1 and O2 on the surface are determined by the results of measurements of the approach polygons (seeFigs. 4.9 and 4.10a). All lengths measured on the surface and in the mine are corrected for calibration, temperature, angle of dip, tape sag, and reduction of lengths to the surface of reference ellipsoid and the

Ch. 4. Connection

54

plane of Gauss projection. The last two corrections are found by the formulae: ASel= (y/2R)s, Aspr = -(H/R)s where y is the mean ordinate of the connection survey region; R is the mean radius of the Earth; H is the absolute elevation; and s is the measured length of the traverse side. The calculated coordinates are used for determining the direction angle of a plumbconnecting line, Qo 0 and the distance bel 2 tween the plummets, c, by the formulae: tanaOlO2

=

(Y°2

-YOl)/(XO2

c = (XO2 -XOl)/COS = (yO

2

-Yo

-XOl)

(4.20)

UOlO:

)/sin 1

Uo O 1 2

(4.21)

or

1, (X

X

02 -01

y--'2 )2

),22 +.,--(y

02 -01

In calculations by formula (4.20), the value of c obtained for the larger increase of coordinates is taken as the final value, whereas that calculated for the smaller increase is used as a check value. Then the coordinates of points of the underground connection polygon are calculated in the conventional system of coordinates. As a rule, the point 01 is taken as the origin of the conventional coordinate system and the axis of abscissaeis directed.along the first side, 01-1. In that case, x'o = y'o = 0 d ' 0 1 1 an

ao1-1= . After that the direction angle of a plumb-connecting line, a' o o , and the dis1 2 tance between the plummets ID the mine, c', are determined in the conventional coordinate system: tana'o o = y'o jx'o 1 2 2 2 ., a o o = x ,o , j sm c,o o = Yo

12

2

12

(4.22)

j cos a,o o

2

12 (4.23)

It is now essential to compare the plummet distances as calculated by the coordinates of the unified system on the surface (c) and in

Surveys

the conventinnal system in the mine (c'). The discrepancy A c = c' -c must not exceed the permissible value A erm which can be found by the formula: Aerm = 2 (mi/p2/[R~;J

+ ~2(SiCOS2
where Rx. are the distances from the points of , the underground polygon to the plumbconnecting line 0102; I.. = 5 x 10-5 is the coefficient of influence of systematic errors of linear measurements; and mfJ is the rootmean square error of angular measurements. Other are the same as in the preceding formulae. The values of R x. are determined on the surveying plan. , If the discrepancy is within the permissible value, all lengths of the underground connection polygon are corrected according to the formula: Asi = -(AC/C)Si (4.25) Then, corrections are determined for the direction angles of the underground connection polygon in order to recalculate this polygon into the coordinate system on the surface. These corrections are found by the formula: Aa

=

ao

o 1

-a' 2

o

o 1

(4.26) 2

The direction angles of the sides of an underground connection polygon will be: ai=ai+Aa

(4.27)

It is now possible to calculate the coordinates of all points of the underground connection polygon from the measured lengths of sides, corrected lengths of sides, and corrected direction angles. The coordinates of a plummet 01 on the surface are taken as the initial coordinates. The r;oordinates of a plummet O2 obtained by the recalculation of the underground connection polygon and on the connection on the surface

Table 4.4. Calculation of Direction Angle and Length of Plumb-Connecting Line in the Coordinate System Adopted on the Surface and in the Conventional Coordinate System Surface coordinate system tan a = Y02 -Y01 Xo -X 2 01

L\y

Ay 0102

L\x

b 13211.868 13325.417 -113.549

YO2 YO1 A.y

9

XOl dx tan

a

a

Conventional

tana' =

coordinate

y' , 02- Y01 x '°

-X ,

, 0,

77810.278 77938.922 -128.644 -128.644 -15.095 -113.549 98.454 1.306641 307°25'39"

YOl +XOl dx+dy

11

64 598.410 64613.505 -15.095 7.522292 262°25'39"

XOl

=

13

dx+dy L\x

14

dy

15 16

L\x-dy tan (a + 45'

17

a+45°

I1x

cosa

c

YO2 +XO2

10

12

3 4 6 7 8

= sina

a 1 2 5

=c

18 20

Ay sin a

22

c

19 21 23 24

-113.549 0.991279 114.548

-15.095 0.131781 114.546 114.548

~x cosa c Cc

system

dy' A uX

.ix'

+ .iy'=

(Y~2 + X~2)

,

cosa' -(y'

+ 01

x'

) 01

Ax' + Ay' tan(a'

25 26 29

YO2 YO1 Ay'

27 28

XO2

30 31 32

tan a'

XOl ':\X' a'

2.224 0.000 2.224

+ 45°) =

33

YO2 + XO2 YO1 + XOl

-114.515 0.000

34 35 36 37 38

-114.515 0.010421 178°53'15"

39 40 41

dx' + dy' dx'

+ dy' dx' dy'

dx'

-dy'

tan (a' + 45°) a' +45°

.,

.-,

-112.291 0.000 -112.291 -112.515 -114.515 2.224

42 44 46

sina'

43 45

d.x' cosa'

-114.515 0.999812

-116.739 0.981898 223°53'15"

47 48

c' c'c

114.537 114.537

da= =a-a'

49 50 51

a

262°25'39"

a'

178°53'15"

da

83°32'24"

Ay'

c'

2.224 0.019416 114.545

"' .:= .. .c CI1

= ... ; ~ > Q ~ E..~ .-=

>, .D ~ Q)

Q)U

= C\SC\S .,g Ou .. = a. .C O .. ~

CI1

..

Q)

~ a. .c CI1 = .~ ~ "3 :i. ..Q) U U C\S tri"E. ..,. >, a. -;.. .c ..=

E-

., e. '" c

'E o o u

"

g~

-"' '"" .:"' .-'" """, '"'"

u.-

'-~ 00 "' ';j "U =0= -;..2 >

.:

-;8 -.0 =0= -0 "'00 Z,-

,",,~ ..,,~

...2.

°uoo.' u"o:

1:1 u ' "' " 0= " .=.9"01, Q-o=

'"

.. B 9 "' ~ .J:: u .., ~

><

...

'<:

tj 8

tj = ';J

8 ~ ~ "' "' ~ ... .. t.s ~ = o S Q) ~ >. "'

2 t.s = ;,s .. o o u Q) -5

.5 "' ;:; S S ~ "E.

." ~ ~

'0 "'

U

:p; 0 O

'; =

Q)

~"O/)CQ. 00 Q "00

~

, "' 0~.5

0, \0

~

on O ~ M -0

M "' M 00 N '-0

~ ""' N M M -

N

~ N N ~ aN t'"I t'"I

""' 0'\ "'") N '0 """ '0

N O O

~ M .r; ..,. I

~ N ..., -

\0 V) \0 ,..; .." I

""' t"'; +

00 00 00 r'") 00 ~ N N

$ ~ +

-0 -.r

~

1-

<=! ""' N

N 00

I

::!:

N I

O

00 N

M

~ M -

Ir) o o ..t I

rrV) 0'1 0'1 O

N 00 ""' o O

-0 ",.

0\ O

'-0 rrr-.: I

~ ...; +

..,. r-. N ~ ~ ~ 0

1/") 0\ 00 00 00 O

~ 0

~ M ~ 01 "'

00 ~ O 00 M ~ 0

""' 0\ 0; "'

1-

01~ -0 -

~

00 00 00 N Ir) o O

~ \r) -t

O M

00 01")

00 0; ~

~ 00 (:7\ (:7\

-

00 00 \0 ; V

o 0

;

00 ~

~

\Q r'"\

0\ v

M O O 00 'r\

ID M

\Q \Q N O M

>

~ N

M

~ '"" .". N

11-

~

11-

'"'"'

'r) 00

O 1'N 0\ 0\ 0\

"'1' \0 \0 "' \0 ~ 0

,..., Ir\ ~ N ~ o O

""

Ir) 0\ N "t'

tr) tr)

>

~

0 0

> -

O ~

-

~ M N

10

~ "'

00 0\

-0 ~

~ N

-0 00

r"': Ir)

..., 0r-0Ir) "! 0

~oo c~

M 00 00 N 00 ID

~

~ = ~ O .. 01) .. 0) O)~ u =

;. "'

'2T ~N "' I 0,; -1i1i 00 ~O)O) ...;. ° "' ~::.::.

:i -o

1'0 0 -6

~ ~ ~ ~ ~ ~

~ ~ 0: ~

~ -.1-

rO O -0

Ir\ Ir\ :!:

~ N "i N

" c

1"-8! o

0

0N "'! a+

0\ "'" tr) tr) tr) 1-

100 -0

~ N Ir\ 0

8 o

~ O ~

~ 0

M 0\ O ." ."

0

~

= >

N N

O

0\ ""'

00 -0 O N "'

>

"" ~ 0 "' "'

~

~ Ir) ~

""' ""' N r..: ""' .,.,

.q. $ N Ir) I IC rN 16 I

00 0N -

\C .,.,

'"") .,., .,., v \C

""' N

N Ir\ Ir\ O -0 :76:76

000 00\ \O1r)

1aI ~ 0;

'0 a0; Ir\ +

~ "' r-O

~ ""' Ir) 0\

00 "' ""' 0 -

~ 0

00 O 0\ I,)

"'" r-r--:

~ 00 00 O

N ." I." ~ 0

-'rl -N 0-,.."

~c;i

-0 t')

.., 'C N

00 ..,

+

O M

N N N

~= 00'1") 00'1") 0\0(")

-\0 N-

O "' M

00

-\0 \ON N,,",

> -

=0 >

-

'Ooo r-'O r-oo r-.:...: MMM """'"'

~o 00-~

:1;

0 r'"\ -0 00 0\

oM 00 M 0~ 0

~ ""' r.: ""' N ""' -

ci

r~ rr~ 0

00 0 -c

~ N ""'

~~ ~rNr0""~ -~

"'" O 0\

~ ~ 0

-Co:t' I -

00

0

:!:

§; ~ I 00 01 M O "' -

""'-

C!

O \Q O

$

""' N .,., ...; oN 00 N -0 Ir)

.,., 0 .,., M

~

0 II") ~

~ O N +

\Q ~ 1"-~ +

~ N ..,. 1-

'0 ~

E ~ N ~.

::0 :z

~ "'

~ >, "'

=

00 M ~ '-0 Ir) N M -

M N ~ ~ +

0

00

~

N 1.0 N

"" "" ~

'00 N '00 00 00 C7) 0

r-aNr~a""\0 ~-

O M

"'" 0

0

00 00 ~ M "1"

-.1--.1NOJ")

r-", NN 00-

O r'"\ r'"\ -

0 0 ~ N 000 0-

:;:; N 0

~ "'" 0

~ I...;

o 0

0~

"' '-0 M 000

'0 '0 !"'j M IJ")

'0 '"'"'

"' ""' 1"-0 N

~

1M ~ 1-

N ~

N M

1-

>

~ N

M QO

>

00 ""'

:::

t' "' ~ I

~ , ,

5: "' M M

N

'I" M N ...; 'I" M M

r'"I -

-

...r'"I O O

C

.-.,., "tj

(,)

8 ~ ;3 "' ..:: t "' ~ ~ -5

.5 ~ ~ ~ >

~ (,) .t: v § = 0 ~ 0 0, bi) .5 'g =

0

= 0 (,) '0 "' = .0 0, "tj = "' "' v E E ;3 '"5. '"' ~ -0; = :0 ... 0 o U

Ir\Ir\ 0\0\ 00 """'"' --

~~ Ir)Ir) ...;...; ---

~~

58

Ch. 4. Connection

can be used for checking. The discrepancy between them must be within the accuracy of calculations. If other methods have not been used for orientation, connection survey via two vertical shafts must be carried out twice. The final result is taken as the arithmetic mean of two procedures. It is recommended to make the connection survey via two vertical shafts in combination with gyroscopic orientation of the sides ading the plummets. An example of calculation for orientation via two vertical shafts is given in Tables 4.4 and 4.5. If a mine field is opened by three or more vertical shafts connected by underground workings, it is recommended to make connection survey through the shafts with the use of redundant measurements. 4.9.

Horizontal Connection Survey with Use of Gyrocomes

The wire of a plummet hanging in a shaft is subject to the action of a number of factors which tend to deviate it from the vertical position. The most important among these factors are air currents in the shaft and underground workings, and abundant water drip (downpour). These factors have been investigated and can be ed for by special formulae. These factors have however become less important with the appearance of gyroscopic instruments which can determine the direction angles of any traverse side in a mine with an accuracy to 10-20". In that connection, geometric methods of orientation now have only a limited application, mainly in the construction of new mines. Repeated orientations in exploited mines are mostly carried out by means of gyrocomes. Further, the essential disadvantage of geometric orientation via a single shaft by means of two plummets is that the distance between the plummets is too short and a direction angle

Surveys

cannot be transferred underground with a sufficiently high accuracy. A practical merit of gyroscopic orientation is that the direction angle of one or several sides of an underground survey net can be determined with a high accuracy in any place of the mine field and at any distance from the shafts. These circumstances have predetermined wide popularity of the connection survey method in which the coordinates x. y of an initial point of an underground polygon are determined by means of a plummet sunk into the shaft, (the problem of projection), and direction angles are then measured by the gyroscopic method. Under production conditions, the problems of centring and projection are tackled separately and in the following sequence. The projection problem is solved by means of a plummet hung in the vertical shaft. The method and equipment in this case are essentially the same as in orientation via a single shaft by means of two plummets. It should be noted, however, that, since the direction angle of the initial traverse side will then be determined by the gyroscopic method, the projection can be carried out in a simplified way without spending time for the stabilization of a plummet, determination of its central positions on scales,etc. on the surface and in the mine. A polygonometric traverse of an accuracy of not less than second-order is run on the surface from the initial side 31-32 to the centring point, i. e. the plummet point ° (Fig. 4.12). The angle ~A at a point A and the distance from that point to the plumb line 0, IAO' are measured in the shaft; the direction angle of a side A-B (IlAB) is then determined by the gyroscopic method. The direction angle of a side O-A is calculated by the formula: IlAO = IlAB -~A :J: 180° (4.28) and the coordinates of the first point (A) of an underground side, by the formulae:

4.9.

Horizontal

Connection

Survey

by Gyrocomes

59

4.9.1. Theoretical Principles of Gyroscopic Orientation

Level950 m Fig. 4.12 Solving projection problem for determining initial point coordinates of underground polygon

XA =

Xo +

loAcosuoA

(4.29)

YA = YO+ loAsin aoA This method is used especially widely at mining enterprises with large mine fields and block-type vertical shafts located at a distance of 5-6 km from the main shafts. The connection survey made by this method increases substantially the accuracy and reliability of the survey reference net in the entire wing of a mine.

Mine surveying has in recent time become less labour-consuming and more accurate due to the appearance of reliable small-sized and explosion-proof gyrocomes. The operating principle of a mine-surveying gyrocom is based on the daily rotation of the Earth and the property of a free gyroscope to rotate freely in three mutually perpendicular planes (Fig. 4. 13). A gyroscope is called balanced if its centre of gravity coincides with the suspension point O (the point of intersection of the three axes). Balanced gyroscopes in which there is no friction in the suspension s are called free. Free gyroscopes can exist only theoretically. Practically, the centre of gravity is always displaced somewhat relative to the suspension axis and there always is friction, though slight, in suspension s. A free gyroscope (Fig. 4.13a) comprises a massive spinning disc, or rotor 2, which is suspended in two gimbals. The rotor is mounted in the inner gimbal 4 and outer gimbal 7 on bearings 1,3, and 5. This system allows the rotor to rotate freely on the

(a)

y

Fig. 4.13

Free gyroscope (a) and pendulum gyrocom (b)

60

Ch. 4. Connection

Surveys

principal (spin) axis x, rotation axis of the inner gimbal y (sensitivity axis), and rotation axis of the outer gimbal z (precession axis). As the disc is rotating simultaneously on the three axes, the suspension point O remains immobile, and the x axis acquires stability and do~s not react to rotation of a base 6, in other words it retains a stable orientation in space. If the moment of an external force is applied to the x axis of a quickly rotating gyroscope, this axis turns (precesses)in the plane perpendicular to the force applied. The angular velocity of precession, O>pr'is directly proportional to the moment of external force M ex and inversely proportional to the rotating velocity H of the gyroscope:

E Fig.

4.14

Components

of Earth's

,x rotation

The principal axis x of a gyrocom set up to a point O at a latitude <Pand at an angle (1 to the meridian will change its O>pr,=M ex/H (4.30) position continuously relative to the horizon If one of the degree of freedom of a plane under the action of Earth's daily rotation, so that its north end will rise gyroscope is restricted, the centre of gravity, which develops an additional pendulum load continuously above the horizon. The principal axis is acted upon by the moment of the on the sensitivity axis y, will displace downward along the z axis into a point O 1. This force of gravity of the pendulum weight, system is called a pendulum gyrocom which is applied in a vertical plane and tends (Fig. 4.13b). A weight Q causes the x axis to to turn the axis in the horizontal plane adopt a position parallel to the horizon towards the meridian. The angular velocity of rotation of the plane. With quick rotation of the system, the x axis is arranged in the meridional plane. horizon plane, 0)3' around the sensitivity axis The daily rotation of the Earth, when obser- y, which underlies the operating principle of a ved from the North pole, is seen to occur gyrocom, is called the useful component of Earth's rotation and can be determined by anticlockwise (Fig. 4.14). As the Earth rotates with an angular velocity 0>,the horizon plane the formula: rotates in space with an angular velocity 0>1 0)3 = O)cos 2 around a vertical line. plane at (1= 00, then 0)3 = 0. At (1 = 90°, 0)3 The angular velocities 0>1and 0>2depend on has the maximum value. The angular velocity 0)3 also depends on the latitude of the station the local latitude 1= o>cos<pand 0>2= o>sin

1, determines variations in the attains a maximum. In all positions, except for that at (1 = 0, height of the Sun and stars above the horizon the principal axis x of a pendulum gyroline and the vertical component 0>2,variacom develops a moment of the gravity tions of their azimuthal positions.

4.9.

Horizontal

Connection

force (guide moment of gyrocom): Mg = H 0) cos
sine

Survey

by Gyrocomes

61

external force, M ex' and the maximum guide moment

Mg

(at

a =

900)

and

can

be found

m~x by the formula: E = Mex/ M g

(4.36) max

The correction E is introduced with a proper sign when calculating the gyroscopic azimuth of a side being oriented. 4.9.2. Mine Surveying

Gyrocomes

There are several types of gyrocomes which can be divided into three groups by the

(4.34)

If the gyromotor is brought into rotational motion, the gyrocom axis will perform continuous harmonic oscillations about an equilibrium position coinciding with the meridional plane. The axis of symmetry of harmonic oscillations relative to the meridional plane is called the axis of the equilibrium of a gyrocom and the positions in which the velocity of motion of the axis is equal to zero and the motion is reversed are called the points of the gyrocom axis. The time during which the gyrocom axis performs a single elliptic oscillation and returns into the initial position is called the period of continuous oscillations of a gyrocom which is expressed by the formula: T= 21t.JH/MO)

cos

(4.35)

Under the action of friction forces, however\ the oscillations of the gyrocom axis are gradually attenuated, the amplitude of oscillations A i decreases,and the pattern of motion of the axis changes from elliptical to that along a twisting helix. This results in a deviation of the gyrocom axis by an angle E from the meridional plane. The magnitude of E depends on the moment of an

Fig. 4.15 General view of gyrocom type MVT2: l-angle-measuring unit; 2-rotatable housing; 3- base; 4- foot screws; 5 -connecting cable; 6-power supply unit; 7-instrument casing; 8gyro attachment; 9-endless micrometer screw

",,' -2

4~

59

~1

4 5

5.2

I II

~.y

/9 c-I0 ! .11 ~

:~ ~ 45-

--12 ---13 1-14 -15

4342414039 383736 35 34-

3332-

Fig. 4.16 Gyrocom type MVT2: 1- autocollimator; 2-illuminating unit; 3-illuminating lamp; 4-illuminating prism; 5-eyepiece; 6-upper rectangular prism; 7- objective; 8 -lower rectangular prism; 9-rectangular prism; 10-upper clamp of torsion suspension; 11- connector assembly; 12 fixed mirror; 13-SE mirror; 14-protective glass; 15-torsion suspension; 16-cable; 17-brushes; 18-collector; 19-cable coupler; 20-1ocking device; 21- gyro attachment fastening; 22- band-type current lead; 23-sensitive element; 24-magnetic screen; 25- gyromotor; 26 ~ gyro unit casing; 27~arrester head; 28-base; 29-base-tuming mechanism; 30-fixed bisector; 31-central hair line; 32-scale; 33-movable bisector; 34-theodolite

-18 ---19 -20 -21 -22 -23 24 -25 -26 -27 -28 -29 -30

---31 Fig. 4.17 Gyrocom type MVT4: 1-explosion-proof glass;2- illuminating lamp; 3- illuminating mirror; 4 -illuminating prism (upper); 5 -illuminating prism (lower); 6-eyepiece; 7-hair cross; 8-upper rectangular prism; 9-lower rectangular prism; 10- objective; 11- worm screw; 12-rhombic prism; 13-protective glass; 14-sensitive element; 15-torsion suspension; 16-locking device; 17-lower clamp of torsion suspension; 18-locking clamp pin; 19-top of locking device; 20-current lead; 21-transducer; 22-damper; 23-top cover of gyro unit; 24-operating mode switch; 25-switch cam; 26-lock; 27-gyro unit; 28-storage battery; 29-battery fastening; 30-balance weights; 31-lower damper; 32- magnetic screen; 33- bottom cover of gyro unit housing; 34- gyro unit housing; 35- button spring; 36, 37 -connecting ring of gyro unit housing; 38 -lower nut of arrester; 39- SE rod; 40- upper cover of gyro unit; 41- tripod leg; 42, 43- tripod head; 44-locking device sleeve; 45-SE mirror; 46, 47-fixed casing of base; 48-control device and upper clamp of suspension; 49- scale; 50- fixed bisector

4.9.

Horizontal

Connection

design, method of centring, and suspension of a sensitive element. I. Gyrocomes with liquid suspension and electromagnetic centring. 2. Gyrocomes with liquid suspension and electromagnetic centring on needle, in explosion-proof or common embodiment. 3. Gyrocomes with torsion suspension, such as types MVT2, MVT4, and MVB4M developed in this country, which are smallsized, reliable and high-precision instruments relatively simple in manufacture and operation. The gyrocom type MVT2 (Fig. 4.15) is intended for the orientation of underground sides in connection surveys and especially for measuring the direction angles of traverse sides in the construction of mine survey reference nets. It belongs to the best instruments in the world designed for mine surveying. The mass of the instrument together with the power supply unit and tripod is 33 kg. The time of start is 30 minutes and the accuracy of measurement of direction angles is 20-30". The gyrocom is positioned by means of a base 3 having a housing 2 which can be rotated around the vertical axis by means of an endless micrometer screw 9. The rotatable housing carries at the top an angle-measuring unit 1 which is essentially an optical theodolite, and at the bottom a gyro attachment 8 in which a sensitive element with gyromotor is suspended from a torsion. The instrument is power supplied from an electric storage battery arranged in an explosion-proof casing. The torsion is made of three strips connected together at flat sides, which makes it possible to obtain a low specific torque. The oscillations of the axis with the sensitive element (SE) about the meridional plane are observed by means of a mirror mounted in the top portion of SE and rigidly fixed to the axis. The standards of the theodolite carry an autocollimator to observe the oscillations of

Survey

by Gyrocomes

63

the SE mirror. The sensitive element can be fixed in the non-working state by an arrester. The observations of forced oscillations consist essentially in taking readings on the circle in the points of reversion and determining the actual position of equilibrium. The design of a gyrocom type MVT2 may be seen in Fig. 4.16. The gyrocom MVT 4 (Fig. 4.17) has been developed on the basis of type MVT2 and has principally the same design. In recent time, a mine surveying gyrocom type MVB4M (Figs. 4.18 and 4.19) has been developed in this country. The designers have managed to reduce the mass and dimen-

Fig.

4.18

MVB4M

General

view

of

gyrocom

type

64

Ch. 4. Connection

Surveys

sions of the instrument and the time for determining a gyroscopic azimuth roughly by 50 per cent compared with the gyrocom type MVT2. In contrast to MVT2, the new gyrocom is intended not only for basic geodetic surveying, but also for everyday (current) mine surveying associated with the construction of underground reference nets and for measuring horizontal angles. Like MVT2, the instrument type MVB4M is a pendulum gyrocom with torsion suspension and comprises a gyro unit, goniometer with multi-faced mirror, and power supply unit (transducer and storage battery) arranged in a common housing which is mounted on a tripod for operation and replaced into a casing for transportation. Tests have shown that the gyrocomes types MVT2 and MVB4M ensure roughly the same accuracy of orientation. Horizontal angles can be measured by the gyrocom type MVB4M with an accuracy of engineering theodolites. Technical characteristics

of gyrocomes MVT2

Error

of

determination

gyroscopic Time side, fors

Fig. 4.19 Gyrocom type MVB4M: 1- gyro unit cover; 2-storage battery; 3-torsion suspension; 4~transducer; 5-catch; 6-current lead; 7- arrester; 8 -locking device; 9- SE magnetic screen; 10- gyromotor; 11-multi-faced mirror; 12~measuring unit casing; 13-mirror for vertical sighting of telescope; 14-rectangular prism; 15-vertical sighting head; 16-teleobjective; 17pentaprism; 18-fixed mirror; 19-photographic objective; 20- hinged mirror; 21- graticule of scale microscope; 22-eyepiece; 23-light filter; 24-illuminating prism; 25-illuminating lamp; 26-illuminating unit; 27- fixed mirror scale; 28- magnetic screen on gyro unit housing; 29-arrester pinion; 30 -lower sleeve of arrester; 31 ~ upper sleeve of arrester; 32- sensitive element; 33 -lower clamp of suspension; 34 -pin with balance weights; 35- upper clamp of suspension; 36- protective cap of upper clamp

azimuth

of

determination

gyroscopic Number

min

starts

without

Mass recharging, of instrument at

least. set

for Number point,

operation kg. of units

a of

azimuth, of

MVB4M

of

at in

..

ready

30

40

20

15

15

10

station the

set.

.

37 3

19 2

The principal design feature of the gyrocom type MVB4M which distinguishes it from type MVT2 and determines the scheme of gyroscopic azimuth of a side, is the provision of a goniometer with multi-faced mirror; this has made it possible to diminish substantially the mass and dimensions of the instrument.

4.9.

Horizontal

Connection

Survey

by Gyrocomes

65

In the modern mining practice where mine fields and dangerous zones are continuously increasing and it is impossible to ensure permanent planimetric positions of points of a reference net, an efficient method for decreasing the influence of angular errors in nets and increasing the reliability of surveying is the introduction of reference nets with gyroscopic polygons in which the direction angles of all sides are determined by the gyroscopic method, i. e. by means of gyrocomes.

side; Go is the gyroscopic azimuth of the initial side; and Yo is the meridian convergence in the station point of the gyrocom on Earth's surface. The gyroscopic azimuths of sides on the surface and in the mine must be measured twice. The difference between the two observations must not exceed 2'. Their arithmetic mean is taken as the final result. The formula for determining a gyroscopic azimuth is as follows: G = (N -N 0) + E (4.38)

4.9.3. Gyroscopic

where N is the reading on the gyrocom circle corresponding to the direction onto a point on the surface or at the underground side being oriented; N 0 is the circle reading at the equilibrium position of the sensitive element; and E is the correction for twisting of the torsion suspension. The junction direction N on the surface or of an underground side is determined twice, at the beginning and end of a start and at two different positions of the vertical circle. The difference between the two measurements should not exceed 30". The final result is found as the arithmetic mean of the two observations. The difference between the direction angle ao and gyroscopic azimuth Go of a side BC on the surface constitutes the gyrocom correction 0. A start in the mine determines the gyroscopic azimuth G of an underground side DE to be oriented. The direction angle of DE is: a = G + 0- Y (4.39)

Orientation

This kind of orientation can be carried out either independently or in combination with other methods. It is obligatory in opening a deposit by means of inclined shafts with angles of dip more than 70°. At least two sides at each mining level must be oriented by the gyroscopic method. In the reconstruction and construction of mine survey reference nets, a side is oriented gyroscopically in each section. The direction angle of an oriented side must be measured independently twice, the discrepancy between the two observations being not more than 2'. The principal diagram of the determination of direction angles by the gyroscopic method is illustrated in Fig. 4.20. In the gyroscopic orientation of a side, it is recommended to make four starts of the gyrocom, the first and the fourth being done on the surface at one and the same side with a known direction angle and the second and third, at the oriented side in the mine. The first start before sinking into the mine and the fourth, after completion of observations in the mine, are performed in order to determine the gyrocom correction (0} which can be calculated by the formula: 8 = no -Go + Yo (4.37) where no is the direction angle of the initial ,-17711

where Y is the meridian convergence for the underground station point of a gyrocom. Substituting from formula (4.37) into (4.39), we obtain: a = ao + G- Go + 01' (4.40) where 01'is the difference of meridian convergencesfor the gyrocom station points on the surface and in the mine, which can be

Ch. 4. Connection

66

Surveys

c IT

, 'g

"io

si

c ..,..0

Ili 1

o

-1

1--

c'

~;I

'Y

c;

r

y

Fig. 4.20 Determination of direction angles of sides by gyroscopic method: BC and DE-respectively initial and oriented sides; B and D-station points of gyrocom on surface and in mine; Ao and A -astronomical azimuths of initial and oriented sides; no and n-direction angles of initial ~nd oriented sides; Cg and C;:-directions of gyroscopic meridians; Go and G-gyroscopic azimuths of initial and oriented sides; L" and C'-directions of astronomical azimuth in points B and D; o-gyrocom correction; 't-measuring unit constant; Yo and y-meridian convergences in points B and D; x and y -rectangular plane coordinates

4.9.

Horizontal

Connection

Survey

by Gyrocomes

67

Fig. 4.21 Determination of gyroscopic azimuth of a side: DE-oriented side; A1. A2, A3' A4 -amplitudes of gyroscopic wobbling of sensitive element; Cg-djrection of gyroscopic meridian; N 1. N 2. N 3' N 4 -circle readings corresponding to reversion points of gyrocom axis; No-circle reading at equilibrium position of gyrocom axis; G-gyroscopic azimuth of side DE; E-twisting angle of suspension

found by the formula: 01'= 1.10YO -I.1Y

(4.41)

where Yo and yare the ordinates of station points B and D of the gyrocom on the surface and in the mine, km (to be found graphically on the plan) and 1.10 and 1.1 are the coefficients depending on latitude (to be found in tables). 5.

If the ordinates of gyrocom station points on the surface and in the mine do not exceed 10 km, then ~o = ~ and formula (4.41) takes the form: 01'= ~o (yo -y) (4.42) The equilibrium position N o of the sensitive element (Fig. 4.21) is found from the observations of four successive points of

68

Ch. 4. Connection

Surveys

Table 4.6. Determination of Equilibrium Position of Oscillating Sensitive Element Reversion points

mean intermediate values

readings

h 10

2 3 4

mean inter. mediate values

readings

divisions 30 35 39 44

30 00 30 00

9 II 9 II

22 24 22 24

38 18 42 28

10 10

23 23 23

28 28 35

divisioru

19.4

41.6 41.9

63.8 20.5 63.4

N o =

10

23

31

no

=

41.7

Table 4.7. Calculation of Junction Direction Junction direction 8

N'

8

10

24

10

36

10

30

8

N"

8

10

08

9

57

10

0.2

N = 8°10'16'

Table 4.8. Calculation of Error for Twisting of Torsion and Suspension

'I',

41.7

N

10

24

15

45.0

N~

10

44

52"

Ho

10

'l'c

+0

2'52"

"',

-0

02

52

07

'Vc

+0

20

40

23

31

D

20

40

20.2

+0

00

53

4.9.

Horizontal

Connection

Table 4.9. Calculation or Gyroscopic Azimuth

Survey

69

by Gyrocomes

Table 4.11. Calculation of Meridian Convergence

N

8

10

16

No

10

23

31

+99.1

+99.3

357

46

45

-1.3

-1.5

E

+0

00

53

G

357

47

38

N -N

o

~ 0.

36.5

-0'50"

36.5 .0'55"

Table 4.10. Calculation of Gyrocom Error Initial sides

points. The correction for twisting of the torsion and suspension is calculated by the formula: E = '11/D (4.44)

Polyamy-Novy 12, 35

40,43

Starts

G~

7

35

l6

Go

17

35

29

B

+0

23

4(j

17

35

22

17

35

35

+0

24

10

where N l' N 2' N 3' and N 4 are the readings on the gyrocom circle at reversion

where D is a coefficient determined as the ratio of the specific guide moment to the specific torque of the torsion and '11:is the twisting angle of the torsion: '11= '11 t + '11 c (4.45) Here '11 t is the zero of torsion suspension determined by the formula '11 t = t (no -nc); t = 52" is the scale value of an autocollimating telescope; no is the suspension zero; and nc is the scale reading of an autocoltimating telescope corresponding to the positiQn of a fixed bisector in the determination of the suspension zero; the term '11 c can be found as the difference of circle readings N c -N o corresponding respectively to the mean value of oriented direction and the equilibrium position of the sensitive element, i. e.: '11 c = N c -N o (4.46) In practice the results of observations and calculations of direction angles in gyroscopic orientation are recorded in a record book (Tables 4.6-4.12).

70

Ch. 4. Connection

Surveys

4.10.

Vertical

Connection

Surveys

km. The height mark transfer should be made independently twice. If the dipping angles of opening workings exceed 5-8°, height marks are transferred by trigonometric levelling. The procedure requires the use of theodolites with the vertical circle accuracy of not worse than 30". Height differences at each side of a traverse line are determined twice: in the forward and back direction. The height mark transfer is performed independently twice. The difference in heights, mm, in this case must be not more than L\h = :t 10~

(4.47)

where nl' n2 is the number of sides in the first and second trigonometric levelling line. Most coal mines are opened by vertical shafts where height marks can often be transferred by means of a long steel tape or length-measuring winch. 4.10.1. Transferring a Height Mark into a Mine by Means of Steel Tape In this method of height mark transfer (Fig. 4.22), the hand winch 4 with a measuring steel tape 7 wound onto its drum "is placed on a temporary platform 3. The tape with a light weight (3-5 kg) is let to sink onto the pit bottom level; then the light weight is replaced by a standard weight 2 corresponding to that with which the tape has been standardized. Measurements are made as required by surveyor's levels 6, set up on the surface and in the mine. Level readings are taken on a staff 1 (asur)set on an initial bench mark R.ur and on a tape 5 (n...r). At the pit bottom level, readings are taken from the station point of the surveyor's level on the tape 5 (nm) and on the staff 1 (llm) set on an underground bench mark Rm. During levelling, air temperature is measured at the surface (t sur)and at the pit bottom level (tm). Then, the position of the tape is

changed by lor 2 m along the height and the horizons of the instruments are changed to make another series of observations. The height difference for each series of observations is found by the formula: hmeas = nsur-nm + asur-am (4.48) The values of hmeasas calculated by two series of measurements must not exceed the permissible deviation L1h = (10 + 0.2H), mm, where H is the depth of a shaft, m. Upon averaging of hmeas'the following corrections are determined: (a) for tape standardization, L1/1, which is taken according to the tape certificate; (b) for thermal expansion of the tape

72

Ch. 4. Connection

Al2 = al(t -to), m, where a is the temperature coefficient of linear expansion of the tape (for steel, a = 1.2 x 10-5); t = 0.5(tsur + tm) is the average temperature of air in the mine; to is the temperature at which the tape has been standardized; and 1 = nsur-nm is the interval measured by the tape in the mine, m; (c) for elongation of the tape under the action of its own mass A13= fyg/2E, m, where y is the density of the tape metal (for steel, y = 7874 kg/m3); 9 = 9.81 m/s2 is the acceleration due to gravity; 1 is the length of the hanging portion of the tape, m; and E is the elastic modulus of the tape metal (for steel, E = 2.5 x 1011Pa); (d) for elongation of the tape due to the different mass of the weights used in standardization and measurements Al4 = 100[(P -Po)/EF], m, where P is the mass of the standard weight, kg; P o is the mass of the weight used in the tape standardization, kg; and F is the cross-sectional area of the tape, mm2. The elevation of a bench mark in the mine, Rm, is determined by the formula: H m = H sur+ hmeas (4.49) where H suris the elevation of the initial bench mark on the surface and h meas is the measured height including all corrections. 4.10.2. Transferring a Height Mark into a Mine by Means of the Measuring .Winch The measuring hand winch shown in Fig. 4.23 has a drum 3 with a steel wire wound onto it. As the handle 5 is turned, a system of rollers 4 rotates the drum and a measuring disc 2 which makes one full turn per metre of unwound wire. The number of full turns is indicated by a counter 1, whereas incomplete turns are indicated with an accuracy to 1 mm on the scale provided at the rim of the measuring disc. In order to measure the depth of a shaft.

Surveys

4

2

~I~iilli~ 5

3

4

Fig. 4.23 Measuring winch

the wire is let to slide over a length measure 1 and a guide pulley 2 into the shaft, and readings are taken on the scales at the beginning and end of the procedure (Fig. 4.24). In depth measurements, aweight-staff 3 with centimetre marks is attached to the end of the wire and the check staff 4 is fastened lor 2 m above the weight-staff (in the top position of the wire, the check staff is not shown in the figure). This scheme of height transfer is much similar to the scheme with the use of steel tape. An observer on the top platform takes the following readings: N sur on the counter and measuring disc scale; tsuron the thermometer of the measuring disc; Asuron the scale of the weight-staff by means of the surveyor's level placed at the station point on the surface; and asur on the staff set up on the initial bench mark Rsurby means of the surveyor's level at the station point on the surface. Then the check staff is lowered onto the level glass of the levelling instrument and all observations are reneated.

4.10. Vertical Connection Surveys

73

These measurements conclude the first stage of observations. After that, the positions of the wire and surveyor's levels are changed and the observations are done in the inverse order, i. e. starting from the pit bottom level. The height difference between the bench marks Rsurand Rm is calculated for each series of observations by the formula: hmeas= Nsur-Nm + asur-am -Asur + Am (4.50)

Fig. 4.24 Transferring height mark into mine by means of measuring winch

The weight-staff is then lowered onto the pit bottom level to take similar readings: N m on the counter and scale of the measuring disc; t m on the thermometer in the pit bottom; Amon the scale of the weight-staff by means of the surveyor's level set up in the pit bottom; and am on the staff placed on the bench mark to be controlled by means of the surveyor's level in the underground station point. As on the surface, these measurements are repeated on the check staff.

If the discrepancy between the observations is within permissible value, the arithmetic mean of hmeas is calculated and the following corrections are determined: (a) for wire diameter fj.ll = 0.0017tdl, m, where d is the wire diameter, mm; (b) for standardization of the disc fj.12 = = (k --'-1) I, m, where k is the actual length of the circumference of the measuring disc as given in the certificate; (c) for thermal expansion of wire caused by the temperature difference in the shaft fj.13 = =0.5all(tm-tsur)' m, where al is the temperature coefficient of linear expansion of wire and t surand t m are the temperatures on the surface and in the mine; and (d) for thermal expansion of the measuring disc considering the difference in temperatures during standardization and measurements, fj.14 = a21(tsur-to), m, where a2 is the temperature coefficient of linear expansion of the disc and to is the temperature of disc standardization. The elevation of the bench mark in the mine (Rm) is calculated by the formula: Hm = Hsur + hmeas+ fj.4 + fj.12 + fj.13 + fj.14 (4.51)

Chapter Five Horizontal

Surveys

of

5.1. General on Underground Mining Surveys The mine survey service of mining enterprises has to tackle matters of timely and accurate determination of the spatial position of undergound workings and all other objects essential for the mining production. The spatial coordinates obtained by mine SUfveying are the basis for compiling and supplementing mining work plans and other kinds of graphical documentation, as well as for the solution of various problems of rational and safe exploitation of mineral deposits. The principal objects of mine surveying are: (a) underground workings (opening, preparatory, development, stoping, draining, exploratory, etc.); (b) boreholes (prospecting, operating, unwatering, water-observation, etc.); (c) boundaries of safe mining work, safety and barrier pillars; (d) contours of inundated, gas-laden, and caved workings, centres of underground fires, isolating partitions and other ventilation structures, gas blower sites, areas and contours dangerous in gas or rock outbursts, rock bump, water inrush, floating earth, sources of underground waters, etc.; (e) characteristic points of bedding elements of mineral deposits (dipping angles, capacity, characteristics of quality and structure); (f) points for documentation of geological disturbances and other textural and struc-

Underground

Workings

tural characteristics of deposits and enclosing rocks; (g) points of mineral assaying; and (h) location of surface and underground artificial structures and stationary equipment in underground workings (hoists, ventilating and pumping plants, various chambers, explosive stores, locomotive sheds, medical service, etc.). The mine survey service solves its problems by constructing reference and survey nets at the mining enterprise. Underground survey nets are understood as a combination of geometrically interrelated polygonometric traverst:s and levelling lines which are balanced (adjusted) tly or separately. Underground reference nets are the principal geometrical basis for making the surveying work and dealing with particular mine survey problems aimed at ensuring rational and safe exploitation of a deposit. The errors permissible in the measurements of horizontal and inclination angles

Table 5.1

20"

0.001

0.00005

0.01

5.2.

Horizontal

Underground

and side lengths in polygonometric traverses can be characterized by the data given in Table 5.1. 5.2. Horizontal Surveys

Underground

The principal kind of horizontal survey in underground workings is theodolite surveying which consists of angular and linear measurements and subsequent calculation of the rectangular coordinates x, y of survey points. The straight lines laid between the mine survey points in underground workings form closed or open polygons, or theodolite traverses. Each theodolite traverse is oriented, i. e. tied to the points of an earlier (initial) survey. Several types of underground theodolite traverses and methods of their connection are employed most often in Soviet mine sur., veying practice, which can be classified by the redundant initial data and the type of (dl

75

Surveys

control. By these features, theodolite traverses may be divided into free and non-free. Free theodolite traverses are referenced to only one point with fixed coordinates and one fixed direction angle; they may be subdivided into open (hanging) and closed. The line of an open theodolite traverse may be stretched (Fig. 5.la) or broken (zig-zag) (Fig. 5.lb). Such traverses are controlled by a repeated theodolite survey. Closed traverses (Fig. 5.1c) are controlled by comparing the sum of the measured angles and the sum of coordinate increases with their analytical values. Non-free theodolite traverses have redundant initial data. They can be run: (a) between the fixed points and fixed direction angles: in that case complete control is ensured in of direction angles and coordinates (Fig. 5.1d); (b) between the fixed direction angles with the initial coordinates of one point, i. e. with control in of direction angles (Fig. 5.le); (el

(Xn+1 ~I 'L~

cr-

(bl

(f)

Fig. 5.1 Types of theodolite traverses: (a), (b), (c) free traverses; (d), (e), (/), (g) non-free traverses

76

Ch. 5. Horizontal

Surveys

(c) between two points with fixed coordinates and with an initial direction angle, i. e. with control by the coordinates of the fixed points (Fig. 5.1.f);and (d) between two points with fixed coordinates, with the initial direction angle being unknown; in that case, control is possible by the length of the closing line of the traverse (Fig. 5.1g). In cases under (b), (c), and (d), a complete control of whether a theodolite traverse has been run properly is not ensured, because of which a repeated traverse is run or the lines and angles are measured repeatedly. Horizontal surveys in underground workings may involve certain difficulties which increase labour consumption, reduce the accuracy of measurements, and increase the error accumulation. Among the principal factors causing such difficulties are: continuous mobility of the underground objects being surveyed and rock displacement around workings resulting in uncertain spatial position of permanent survey points underground; certain limitations in selecting the most favourable shapes (schemes) of theodolite traverses and the best lengths of traverse sides (some sides may turn out to be too short); constricted conditions for surveying in underground workings; poor illumination of working places; dust-Iaden atmosphere in mines; etc. In order to minimize the influence of the factors indicated on the accuracy of surveys and to avoid unproductive labour expenditures, it is essential to adhere to the following main principles in surveying work: I. Mine surveying should proceed from the more general and more precise procedures to more particular and less accurate work, i. e. it should start from constructing reference nets, after which survey nets are plotted, and finally, the surveys of particular mining objects and other details are performed. 2. In any kind of surveying work, all measurements must be done with the

of Underground

Workings

optimum accuracy sufficient for the purpose. An insufficient accuracy can spoil the survey work and require unjustified expenditures on its amendment; in some cases, inaccurate survey work can have serious consequences endangering the safety of mining workers. On the other hand, an excessive accuracy involves a large loss of labour and time of surveyors on unproductive and uselesswork. That is why the mine surveyor must be able to select pro~rly the suitable method of surveying and the required accuracy. 3. Mine surveying must be carried out under an appropriate and timely control both in the field (in underground workings) and in the office analysis of the results of surveys. First of all, it is essential to make a check, or control, before starting a surveyor continuing a theodolite traverse, i. e. to measure the horizontal angle of an earlier survey in the junction points. The difference between the initial value (known from the earlier survey) and the measured value of a control angle must not exceed I' for the theodolite traverses of a reference net or 2' for the traverses of a survey net. With a larger difference in the measured control angle, it should be supposed that the points of the earlier survey have been displaced and the projected theodolite traverse must be tied to other points which are known to be stable. The elements of a survey (side lengths, angles, height differences) must be checked in the course of survey measurements so that probable errors can be revealed and corrected in situ. For instance, when measuring distances, control can be ensured by measuring forward and back; in angular measurements, a check reading on the circle can be taken, etc. The measured angles of a closed polygon (traverse) can be checked by comparing the sum of angles with their analytical sum. The measured lengths can be checked by the discrepancies in coordinate increases and by other methods of control.

5.3. Underground

Reference Nets of Plan Control

For reliable and efficient performance of mine surveying, it is essential, before starting the work, to study carefully the conditions of the field work, to draft the plan of construction of survey traverses by the results of reconnaissance and consider in it the existing peculiarities, narrow places, etc., to determine the set of surveying instruments and equipment, to test and adjust the instruments, to assign performers for the survey work and acquaint them with the survey work plan, and, when required, to make preliminary calculation of the accuracy of surveys. 5.3. Underground Reference of Plan Control

Nets

Underground reference nets of plan (horizontal) control are the principal geometric basis for all horizontal angle-measuring surveys. They are created in the principal opening and advance workings (adits, inclined shafts, crosscuts, inclines, brake inclines, fringe, group and haulage drifts) by running the theodolite traverses of a particular system. The system of construction of reference nets can be characterized by certain specific features, in particular as regards the shape of polygonometric traverses, provision of additional ties, lengths of sides, and number of fixed direction angles. Depending on the bedding conditions of deposits and methods of opening, there are six principal systems of construction of underground reference nets which are employed in Soviet mine surveying practice (Fig. 5.2). I. The scheme of construction of a reference net for working a single horizontal seam is shown in Fig. 5.2a. This scheme is typical for deposits opened by vertical central doubled shafts and is essentially a system of polygonometric (theodolite) traverses run in the drifts of main directions and other

workings parallel and perpendicular to them. 2. In working of single gently dipping and inclined seams where the deposit is opened by inclined shafts and ventilation shafts are driven at the flanks of the mining field, it can be distinguished between two versions of a reference net depending on the working system employed: (a) with a continuous working system, theodolite traverses are run twice in level drifts (Fig. 5.2b); (b) with the system of longwall retreating on strike, survey traverses form closed polygons ading one another (Fig. 5.2c). With advancement of mining work in the systems indicated, theodolite traverses are connected to the initial fixed points on the surface. 3. In mining a suite of gently dipping or inclined seams where the deposit is opened by vertical central doubled shafts with a main crosscut and ventilation shafts are driven at the flanks of the mining field, two versions of a reference net are possible: (a) theodolite traverses form a system with junction points (Fig. 5.2d); and (b) if a longwall mining system is employed, the reference net includes theodolite traverses with junction points and closed traverses (Fig. 5.2e). 4. In mining a suite of steeply dipping seamswhere the deposit is opened by vertical central doubled shafts with a main crosscut, the construction of a net depends on the location of mine workings on the main levels: (a) a system of closed-traverses ading one another; such nets can be formed in mining a suite of seams where the fringe or group haulage drifts and auxiliary crosscuts are driven (Fig. 5.2./); (b) a system of polygons with closed traverses and repeated control traverses. This version may appear in mining a suite of thick steep seams liable to self-ignition, which requires that fire pillars be left between the workings (Fig. 5.2g).

78

Ch. 5. Horizontal

Surveys

of Underground

Workings (c)

(b)

(f)

(e)

[~I~ 1-L---

5. In high-capacity ore deposits where vertical shafts are driven both in the centre and at the flanks, theodolite traverses are run in crosscuts and fringe drifts and connected to the points of plummets hung in vertical workings (Fig. 5.2h). 6. In underground mining of salt deposits opened by vertical central doubled shafts, a reference net is Conned as a system of ading closed polygons (Fig. 5.21). The considered systems of construction of reference nets have certain essential drawbacks in view of the specifics of mining conditions: (a) redundant fixed direction angles, sides and coordinates may be limited in number or even absent. As a rule, the orientation of reference nets is most often carried out in the

~:=

centre of a mining field; further, some sides of theodolite traverses may turn out to be too short. These factors lead to substantial error accumulation and non-uniform accuracy of a net; (b) if the reference net points are displaced and the number of additional ties (fixed coordinates and fixed direction angles) is insufficient, then a need arises to run an appreciable number of repeated theodolite traverses. In existing systems, and the more so, with ever increasing dimensions of mining fields and mining depths, these drawbacks become especially sensible. This circumstance has led to the appearance of more advanced systems of construction of underground reference nets with autonomous orientation of a net by

5.4.

onstruction

r~-r-r-I I I @---6-L-1--b-L-

Reference

(b)

(a)

1 2 3 -:§)- -;:::)-

of Underground

---C](d)

~

@

'0-

I

~ ---{::J-

5.4. Construction of Underground Reference Nets Underground reference nets are constructed according to an engineering design which should consider the actual positions of the existing mining workings and their expected development and establish the most favourable system of the net, the distances between the sides with reference direction

@):::J

, ..d

r§r ~ Fig. 5.3 Examples of arrangement of sides with reduridant direction angles: l-initial 3- side with redundant direction angle

gyroscopic instruments, i. e. with inclusion of redundant (fixed) direction angles (Fig. 5.3). The mine surveying practice quite often uses free hanging theodolite traverses run twice. In order to avoid the need in running a repeated traverse in autonomous determination of direction angles by a gyrocom, a polygon is divided into sections (Fig. 5.3a).In a similar manner, additional ties can be included into the theodolite traverses between two fixed sides (Fig. 5.3c). In ading. free closed traverses of large extension, the reference direction angles are measured in each closed traverse (Fig. 5.3b). In non-free theodolite traverses controlled by point coordinates, a repeated survey is done by measuring the direction angles of the sides ading the points (plummet points) with fixed coordinates or the sides close to them (Fig. 5.3d). A similar construction of a reference net with additional ties is possible in a version when the net is developed from a junction point to points with fixed coordinates (Fig. 5.3e).

79

(cl

I

(e)

-J-

Nets

side; 2-traverse;

angles, points and methods of junction of the constructed net to the reference net on the surface, points for setting up permanent station marks, and the order of net adjustment. The work of construction or reconstruction of a reference net is carried out in the following order: (a) reconnaissance is carried out in underground workings and permanent station marks are revised, located and fixed; (b) the sides of a net are oriented by gyroscopic instruments; (c) angular and linear measurements in theodolite traverses are carried out; (d) the net is centred and the theodolite traverses are connected to the points of the mine survey reference net on the surface; (e) the results of measurements are processed preliminarily and estimated for accuracy; (I) the net is adjusted and the point coordinates are calculated; and (g) the coordinates of permanent station marks are recorded in a list. The object of reconnaissance is to investigate the underground workings in which the reference net has to be constructed, to specify the system of the net, and to choose places for setting up permanent station marks. It is also essential to consider the conditions under which permanent station marks will be preserved longer and will be convenient for survey work. Permanent station points are set up in groups of three or four. The spacings between the points in a group are usually equal to

80

Ch. 5. Horizontal

Surveys

50-100 m and the spacings between the groups must be not more than 500 m. The chosen places for setting up permanent and temporary points are fixed in the underground workin~ and on sketches. The orientation of underground reference nets is carried out by means of small-sized gyrocomes. These instruments offer the possibility for constructing a reference net as a system with intermediate (redundant) direction angles and a system of local nets, in particular at the mining field flanks. The essenceof the system of a reference net with redundant direction angles consists in that a polygonometric net of a length more than 2 km is divided into sections with fixed (gyroscopic) direction angles. The number of angles in section should be not more than 20. The direction angle of one of the sides is measured by a gyrocom independently in each section, and the results of angular measurements are combined and adjusted. The direction angles of the sides in the sections determined in this way are taken as fixed angles and their relative weights are considered. Nets with redundant direction angles have an advantage of being more uniform; further, the positions of the remotest points of a net can be determined with a higher accuracy. Calculations have shown that the accuracy of the final point of a theodolite traverse of a length of 5000 m, divided into sections (of a length of 1 km), increases by a factor of seven. Besides, it is possible to control the errors in the positions of the points of a net within wide limits in accordance with the location of the sides having redundant direction angles, which increases the reliability of the net. In mine survey reference nets, gyroscopic sides are located roughly in every 20 traverse sides. In order to check 1hat the locations of gyroscopic sides in a projected reference net are chosen properly, calculation is carried out to determine the error of location of the

of Underground

Workings

remotest point of the net, considering the supposed (planned) development of mining work (usually for 5-7 years). The root-mean square error of location of a point relative to an initial point A of a reference net (Fig. 5.4) can be determined by the formula:

+(Lrf)n

+

(Lrf)k

where I and II are the numbers of sections, k is the number of the last section of a net; ~ and A. are the coefficients of random and systematic influence in side length measurements by a tape; ii is the length of a traverse side, m; L is the distance between the points A and 1; m; mp and m« are the rms errors of a turning angle 13and direction angle a; r i is the distance from a theodolite traverse point to the centre of gravity O of the given section, m; R is the distance from each point of a hanging traverse to the final point 1; m; D are the lengths of intervals connecting the points A and T through the centre of gravity O of the net sections, m; and p" = 20~65". The coordinates of the centre of gravity of a section are calculated as the arithmetic mean of the coordinates x, y of points in the

5.5.

Survey

section. The values of I, L r, R, and D are found on the plan of the projected net. In cases when the mining work is carried out at distances more than 1.5-2 km from the shafts of a mine and the points of a survey reference net are subject to displacements, local reference nets are constructed at the flanks of the mining field and oriented by the gyroscopic method. The horizontal angles in polygonometric traverses of reference nets are measured by theodolites reading with an accuracy not worse than 30". The rms error of angular measurements must not exceed 20". When polygonometric traverses are run in underground workings with dipping angles up to 30°, horizontal angles (forward to the left) must be measured by the method of sets or, in extreme cases, by the reiteration method. In the latter case, the difference between a check value and final value of an angle must not exceed 45". If angles are measured by the method of sets, the discrepancy between the half-sets must be not more than 60". In undergound workings with dipping angles more than 30°, horizontal angles must be measured only by the method of sets (not less than two) under the observance of the following rules: (a) before each set, the instrument is centred once more and the vertical axis is set truly vertical; and (b) before making a second set, the initial reading is shifted by 180°. With measurements in underground workings with dipping angles more than 30°, the discrepancies between the angles measured in individual sets must not exceed the values given in Table 5.2. The side lengths in theodolite traverses can be measured by standardized steel tapes (of a length of 20 m, 30 m or 50 m), linen tapes or light range finders. In length measurements by steel tapes, each side must be measured twice (forward

81

Nets

Table

5.2

Permissible angular discrepancy between half-sets, min at junctions between horizontal and dipping workings 31-45 46-60 61-70

1.3 1.8 2.5

in dipping workings

2 2.5 4

and back) and the discrepancy between the two measurements must not exceed 1/3000 of the side length. The sides of a length more than 50 m are recommended to be measured by light range finders. If the discrepancy between the readings of a measured length in the first and second phase does not exceed 2-3 mm, the measurement can be limited to a single set. The maximum discrepancy between the measurements at different frequencies must be not more than 8 mm. The engineering design for mine surveying should specify that the error in the location of the remotest point of the underground net relative to the initial point of the underground reference net or the closest points of that net on the surface should be not more than 0.8 mm on the map or plan. This requirement is dictated by the specified accuracy of graphical construction of mining work plans. As is known, the permissible error of the position of a contour point of the walls of the main working on a plan relative to the points of a mine survey reference net on the surface is taken to be equal to 0.8 mm, while the positions of the walls are determined by taping directly from the net points with an accuracy to 5 cm. 5.5.

Survey

Nets

Underground survey nets are the basis for surveying of mining workings and solution of

82

Ch. 5. Horizontal

Surveys

Table 5.3 Type of traverse

Theodolite Goniometer

mp

40" 10'

m,

60" 10'

Pernlissible discrepancy between two measurements of side closed 1/1500 open: 1/1000, 1/200

of Underground

Workings

tween the check and final values of an angle must not exceed 1.5'; in the method of sets, the discrepancy between two half-sets must be not more than 2'. The angles in the workings with dip angles more than 300 must be measured in two rounds with resetting of the initial reading roughly by 180° before the second round. In goniometer traverses, angles can be measured by goniometers or theodolites in a single repetition or set. The permissible discrepancy between the check and final values of an angle or the discrepancy of angles in half-sets must be not more than 5'. Before starting a theodolite or goniometer traverse, a check measurement of the last angle of the previous run is made. The discrepancy between the earlier and current measurements of this angle must be not more than 2' in theodolite traverses or 8' in goniometer traverses. The side lengths of theodolite traverses are measured by standardized steel tapes twice, shifting the tape after the first measurement. It is permissible to make both measurements in the same direction. The deviations of intermediate plumb-bob lines from the traverse line must not exceed 1/200 of the length of the smaller interval. Tape readings are taken to a millimetre. In goniometer traverses, side lengths can also be measured by linen tapes or optical range finders with a relative accuracy not worse than 1/300. Tape readings are taken with an accuracy to a centimetre.

problems of mine geometry and are constructed in the form of theodolite and goniometer traverses. Theodolite traverses are run in all preparatory workings except for those in extraction sections and blocks which can be surveyed by goniometers. The permissible root-mean square errors in measurements of horizontal angles mp and inclination angles m" are given in Table 5.3. The points of a theodolite traverse serve as the basis for tackling various problems of mining geometry within the limits of a block or and for surveys of indicated workings. Goniometer traverses are developed on the basis of theodolite traverse points and serve as the basis for surveying of preparatory and stoping workings. The fixed points of a theodolite or goniometer traverse in these workings are used only once in surveying of these workings or for connection of preparatory workings within the limits of a face. Theodolite and goniometer traverses in survey nets are usually c.osed or are run twice. When theodolite traverses are run in main workings to supplement the plans for further development of reference nets, it is permissible to run free traverses with mea5.6. Types of Station Points surements of left and right forward angles of Reference and Survey Nets. (except for workings approaching pillars or Their Fixation dangerous zones). The angles in theodolite traverses are Depending on the purpose and existence measured by theodolites. In theodolite tra- term of a survey net, the points of theodolite verses run in the workings with dip angles surveys (station marks) are divided into less than 30°, angles are measured in a single permanent and temporary. repetition or set. If angles are measured by Permanent station marks are the basis for the repetition method, the discrepancy be- the development of reference nets. They are

5.6. Station

Points

of Reference

established in the bottom and robf of underground workings so as to ensure their stability and existence for a long time. In view of this, permanent station marks are established where possible in the areas beyond the zones of influence of pressure or underworking, weak enclosing rocks and rocks liable to heaving. Some types of permanent station mark for establishing in the footwall of workings are illustrated in Fig. 5.5. A permanent station mark usually consists of a metallic rod 25-30 mm in diameter and 200-700 mm long which is concreted in a drill hole (Fig. 5.5a) or pit (Fig. 5.5b and c). The top face of the rod is marked by drilling a hole or by punching a circular (up to 2 mm) or cross-wise mark. For longer preservation, some types of permanent station mark have a pressed-in copper or lead plug at the top, with a punch mark made in it. Permanent station marks established in the roof of workings should be convenient for plumbing a theodolite under them. For this purpose, they have a drilled hole around 2 mm in diameter for ing the line of a plumb bob (Fig. 5.6). Permanent station marks and special bench marks can also be established in the side walls of underground workings. They are usually fixed by concreting.

and Survey

Nets

83

Temporary station marks are fixed in the roof of underground workings, top beams of frames or on steel arcs. If a working is driven in a hard rock without ing, a station mark (centre) can be fixed directly in the roof rock (Fig. 5.7a) or in a wooden plug driven into a cut hole (Fig. 5.7c). Figure 5.7b shows a station mark to be fixed on wooden s and Fig. 5.7d, a mark for fastening on metal lining.

Fig. 5.6 Pennanent station marks for setting in roof of underground workings: (a) in concrete; (b) in wooden plug; (c) hole for plummet line

84

Ch. 5. Horizontal (a)

Surveys

of Underground

Workings

(c)

(bl

(dl

t++~ ~

Fig. 5.7

Temporary

station

marks

Station marks in underground workings are fixed so that a plumb bob can be hung quickly and conveniently and the plumb line be always in the same position. For quick identification of permanent and temporary station marks, metal plates (markers) with their numbers are fastened on props or on the opposite side walls of a working. In underground workings without ing or with concrete lining, the numbers of station marks are marked on the side walls by an oil paint using a template. Upon establishing of permanent and temporary station marks in underground workings, their positions are marked on sketches in the surveyor's field book and in coordinate calculation book. The established permanent station marks are transferred onto the mining working plans. Each kind of permanent station marks is provided with a certificate. All permanent points must be numbered.

5.7.

Theodolites

Theodolites are the principal type of an instrument for making underground angular surveys.

-g~ Mining theodolites differ from those employed for surface survey work in certain design features associated with the specific conditions of surveying in underground workings. The principal parts of a mining theodolite should not corrode under the action of chemically aggressive water. They should have small dimensions and low mass and be provided with illuminating devices. The optical systems should be hermetically sealed to prevent mechanical damage and penetration of dust and moisture inside. The possibility should be provided for automatic centring and for mounting of a theodolite and signals on tripods and console holders. The telescope of a mining theodolite usually has an upper centre (thorn) for centring the instrument under a station point by means of a suspended plumb bob. It should permit focussing onto objects beginning from a distance of lor 2 m. Mining theodolites should allow the measurement of inclination angles up to 90°, because of which some models are provided with an eccentric telescope in addition to the central one. Theodolite, type T2 (USSR), is a precise instrument with a rotating limb and two-

5.7. Theodolites

85

sided optical wedge-type micrometer. The ja) instrument has coaxial sighting devices, an optical centring device, and a detachable tribrach which permits surveying by a three-stand scheme.The telescope is provided with two optical sighting devices for rough aiming at objects. By the consumer's request, the instrument can be supplemented with a box com, striding level, two-sided optical centring device, eyepiece attachment, range finder attachment, and other auxiliaries. The theodolite is designed for class-3 and class-4 triangulation and polygonometry and can measure horizontal angles with an accuracy to :t: 2-3". Theodolite, type 2T2 (USSR), shown in Fig. 5.8a, is a more advanced model and differs from the former in the following: the system of a vertical axis is non-repeating; the reading device takes readings from two diametrically opposite sides of angle-measuring circles, which eliminates the effect of eccentricity of these circles: for more convenience, the field of view of the reading microscope shows additionally the numbers of tens of minutes; and the telescope gives a better image. The tangent screws are set coaxially with winged-knob clamp screws. Both pairs of screws are arranged at the same side of the instrument for a quicker change from azimuth-sighting to vertical plane-sighting of the telescope. The telescope graticule has two horizontal hairs (stadia hairs); one of the vertical hairs is doubled. The horizontal and vertical circles of the theodolite have 20'-value graduations and 10 numbering. The horizontal circle has double Fig. 5.8 Theodolite, type 2T2: (a) general view; (bifilar) graduation lines and the vertical one, 1 ~objective; 2-optical sighting device; 3 -micrometer head; 4- vertical clamp; 5- vertical tangent single lines. The images of graduation lines and screw; 6- horizontal clamp; 7- horizontal tangent numbers are projected in the field of view of screw; 8-clamp screw of base (); 9adjusting screw of vertical circle level; IO-level the reading microscope by means of a tube; Il-horizontal circle aperture; (b) field ofvi~w double-channel optical system. Changing of scale micrometer (reads 17o 25' 26.5" on from one optical channel to the other is horizontal circle)

86

Ch. 5. Horizontal

Surveys

performed by means of a handle. With the handle set horizontally, the field of view of the microscope shows the images of the double lines of a horizontal circle and with the vertical position of the handle, it shows the lines of the vertical circle. The field of view of the reading microscope is shown in Fig. 5.8b. The central aperture shows the images of graduation lines of two diametrically opposite sides of a circle, which are separated by a halving line. The upper aperture shows numbered degrees and below them, a scale of six numbers (from O to 5), which indicates tens of minutes. The aperture at the right is the micrometer scale with one division corresponding to one second of the arc. To take a reading, the micrometer head is operated to align carefully the top and bottom images of the lines of a vertical circle or respectively those of the double lines of a horizontal circle. If two numbers of whole degrees are seen in the upper aperture, the true one is that which does not beyond the limits of the ten-minute numbered scale. The number on this scale just below the degree number gives tens of minutes. Then, whole minutes and seconds are read off respectively on the left-hand and right-hand part of the micrometer scale. c It should be noted that before aligning the vertical circle graduation lines, it is required to align the ends of the level bubble image by an adjusting screw. Theodolites T5 and T5K (USSR) are precise instruments with a cylindrical repeating system of vertical axes. The horizontal circle can be locked with or unlocked from the alidade by means of a repeater lock. The repeating system of vertical axes allows horizontal-angle measurements by the method of reiteration or the method of sets. These instruments are designed for measuring horizontal and vertical angles in underground workings when constructing reference nets and on the surface in analytical

of Underground

Workings

Fig. 5.9 View field of scale microscope of theodolite, type T5 (reads: 74 o 55.0' on horizontal circle and 12 o 06.0' on vertical circle)

and polygonometric nets of the lst and 2nd order. The theodolite TSK differs from TS by the provision of a compensator whicb automatically eliminates the error in measured vertical angles, caused by the deviation of the vertical axis of the instrument. The working angular range of the compensator is ::t 3'. In view of this, the vertical circle alidade has no spirit level. The compensator also ensures precise levelling of the collimation axis of the theodolite, and therefore, the instrument can also be used as a level. The high-quality telescope of theodolites TS and TSK has a magnification of 27 and the focussing range from 2 m to infinity. Optical sighting devices for rough aiming of the instrument are provided at the top and bottom of the telescope. Precise aiming of the telescope is effected by means of tangent screws. The angle-measuring circles have I-degree graduations. Readings are taken by means of a scale microscope arranged near the telescope eyepiece. The scale microscope shows simultaneously the graduation lines of

87

5.7. Theodolites

the vertical and horizontal circle (Fig. 5.9) and its scale is graduated to single minutes. Angles are measured by reading off the degrees on the limb scale and the minutes on the microscope scale; the seconds are estimated by eye as a fraction of the microscope scale division. The reading accuracy is equal to 0.1 of the scale value of the microscope, i. e. :t 0.1" or :t6". Theodolites 2TS and 2TSK (2TSKP) (USSR) are further modifications of type T5. These instruments are of the non-repeating type. In the theodolite, type 2T5K (Fig. 5.10a), the functioncof the level of the vertical circle alidade is performed by ap optical compensator with a self-adjusting index. Angles are read off at one side of the circles. For easier calculation of vertical angles, the vertical circle is numbered in sectors from 0 to 75° and from 0 to minus 75°. The tangent screws of the telescope and vertical circle alidade are coaxial with the corresponding winged-knob clamp screws; both pairs of screws are arranged at the same side of the theodolite. The telescope is fully reversible, i. e. can be transited at both ends, and focussed by means of a rack-and-pinion gear. The eyepiece can be adapted to the observer's vision by means of a diopter ring which should be rotated until the cross hairs are seen sharp. The two extreme horizontal lines of the cross hairs (above and below the cross) are stadia hairs. The telescope is provided with two collimation sights for rough pointing to objects. When using a sight, the observer's eye should be at a distance of 25-30 cm from it. For aiming at an object, the telescope is rotated on the horizontal axis and the theodolite body, on the vertical axis. Precise aiming is made by operating micrometer tangent screws 5 and 7 when winged-khob clamp screws 4 and 6 are locked. A special handle is provided for changing the sections of horizontal circle (in angular measure-

Fig. 5.10

Theodolite,

type

2T5K:

(a)

general

view; l-objective; 2-optical sighting device; 3 -level tube; 4- vertical clamp; 5- vertical tangent screw; 6- horizontal clamp; 7- horizontal tangent screw; 8-clamp screw of base (); 9-foot screw of base; IO-horizontal circle aperture; (b) view field of scale microscope (reads 127 o 05.6' on horizontal circle and 0 o 34.0' on vertical circle)

88

Ch. 5. Horizontal

Surveys

of Underground

Workings

ments). To change from one section to measuring the horizontal and vertical angles another, the handle should be turned and at in theodolite and tacheometric traverses, for the same time pressed down along its axis. the construction of plan and elevation survey The setting of the horizontal circle in a nets on the surface and in underground particular section is additionally controlled workings, and for measuring distances (by by indexing in the aperture of horizontal using the stadia hairs of the telescope). circle finder. These theodolites have a repeating system The horizontal and vertical circles have for measuring horizontal angles by the I-degree numbered graduations. The graduareiteration method and are convenient for tion lines and numbers are projected in the asg directions to mine workings. plane of reading scales of the microscope. The principal parts and units of the instruThe image of the vertical circle is tinted blue ments are protected against dust, dirt and and that of the horizontal circle, yellowishmoisture. The telescope can be plunged green. The illumination of the field of view (transited) at both ends. It is of the internalcan be controlled by a hinged mirror. The focussing type and is focussed by rotating the scales are focussed for distinct vision by eyepiece ring. Optical sighting devices arranrotating the diopter ring of the microscope ged at both sides of the telescope serve for eyepiece. rough aiming at objects. Precise aiming is The field of view of the microscope of done by means of a micrometer screw and theodolite 2T5K is illustrated in Fig. 5.10b. tangent screws when the corresponding The images of the reading scale and the clamp screw is locked. The eyepiece of the vertical and horizontal limb are projected microscope for reading off on the horizontal respectively in the upper and lower apertures and vertical circles is located near the teleof the field of view. Each division of the scope eyepiece. reading scale corresponds to one minute of The vertical axis of the theodolite is set the arc. The fractions of minutes can be truly vertical by means of bubble level which estimated by eye with an accuracy to 0.1 of a is centred by adjusting screws. division. The reading index is the hair of the Theodolites of these types have a hollow limb. Th~ reading error is equal to 0.05-0.1 of vertical axis for centring over a station point a scale division, or 3-6". The readjng scale of by means of telescope. The eyepieces of the the vertical circle has two rows of numbers. telescope and reading microscope are proviThe lower row (with the minus sign) is used ded with zenith attachments which permit for reading off when the vertical limb hair the observations of objects at angles above with the same sign is seenin the reading scale 45° to the horizon and theodolite centring aperture. over a point. A diagonal eyepiece (optional) The certified accuracy of angle measure- can also be used for zenith and nadir sighting ment ( :1:5") is ensured in measurements by and centring over a point. the method of full sets (with the instrument Theodolites, types T30 and 2T30, are positioned 'face left' and 'face right'). In order mainly designed for surface surveying, but to eliminate the division error of the horizonare often employed for surveys in undertal circle, the latter should be reset after each ground workings. full set by 180°: n (where n is the number of Theodolite type T30M (USSR) shown in full sets). Fig. 5.lla is a mining theodolite. It has a Theodolites T30, 2T30, and T30M (USSR) specially designed vertical axis (spindle) and a are angle-measuring instruments of technical reversible bubble level for the operation of precision ( :1:30"). They can be employed for the instrument in both upright and inverted

5.7. Theodolites

"" Fig. 5.11 Theodolite, type T30M: (a) general view; 1- theodolite base; 2- horizontal clamp; 3- horizontal tangent screw; 4- illuminating attachment; 5- diopter ring; 6- microscope eyepiece; 7- telescope focussing ring; 8- optical sighting device; 9-telescope clamp screw; 10-vertical tangent screw; 11 -level tube; 12 -lever for locking of horizontal circle with alidade; 13-1ock; 14-zenith (prism) attachment; 15- diagonal eyepiece;(b) view field of scale microscope (reads 23 o 54' 30" on horizontal circle and 150 12' 30" on vertical circle)

89

positions, which is essential in underground surveys. The sighting devices on the telescope have a centre mark for centring (plumbing) the instrument under a point by means of a plumb bob. For ease of operation in underground workings, the reading scales are provided with an illuminating system which can be switched on by a button either for a short time to take a reading or for continuous illumination. The reading microscope arranged near the telescope eyepiece has the field of view in which the images of the vertical and horizontal circles are projected simultaneously (Fig. 5.llb). The reading scales have 60 oneminute divisions. The graduations of the vertical circle (limb) are projected against the upper reading scale in the field of view and those of the horizontal circle, against the lower scale. A reading can be taken by eye estimation to 0.5 or 0.25 of a division, i. e. with an accuracy to 30" or 15". A version of the former instrument is type T30ME theodolite with an auxiliary eccentric telescope (Fig. 5.l2a); an eccentric telescope with a bracket is also obtainable optionally to the type T30M theodolite (Fig. 5.l2b). Theodolite, type T30ME (with an eccentric telescope) i\ designed for surveys in steep underground workings and for surface surveys connected with sighting of the telescope in the directions close to the vertical. The eccentric telescope has the same optical characteristics as the central telescope and is also provided with optical sights. Theodolite TheoO1O(GDR) is a precision instrument provided with a rotating limb, a lens-and-mirror telescope, and a two-sided optical wedge micrometer. It has a detachable tribrach and an optical plummet. The advanced versions of this instrument, Theo010A (Fig. 5.l3a) and TheoOlOB, have an opticomechanical compensator of the vertical circle and an erect-image telescope. The field of view of the reading microscope of type

Fig. 5.12 Theodolite, type 2T30ME: (a) general view; l-central telescope; 2-eccentric telescope; 3 -level tube; 4- horizontal clamp screw; 5- horizontal tangent screw; 6- base clamp screw; 7- vertical clamp screw; 8-focussing rack-and-pinion; (b) eccentric telescope to theodolite, type 2T30M (b) (a)

.

/1

46""

,10 5

.3 78-

9-

Fig. 5.13 Theodolite, type Theo010A: (a) general view; 1 -objective; 2- optical sighting device; 3- optical centring device; 4 -micrometer; 5 -vertical and horizontal clamps; 6-circle switch; 7, 8-vertical and horizontal tangent screws; 9-foot screw; lO-illuminating mirror; (b) view field of scale micrometer (reads 112o 27' 35.0" on horizontal circle)

5.7. Theodolites

91

lb)

Fig. 5.14 Theodolite, type Theo020A: (a) general view; l-objective; 2-optical sighting device; 3-optical centring device; 4-eyepiece; 5-vertical and horizontal clamps; 6- disconnection of vertical circle; 7-illuminating mirror; 8-vertical tangent screw; 9-horizontal tangent screw; IO-foot screw; (b) view field of scale microscope (reads 235 o 050' on horizontal circle and 256 0 52.0' on vertical circle)

TheoO1O theodolite is shown in Fig. 5.l3b. These instruments are intended for triangulation and polygonometry on the land surface. Theodolite TheoO20 (GDR) is a repeating theodolite of technical precision. It has an optico-mechanical compensator on the vertical circle (instead of a bubble level), an optical centring device, and a detachable tribrach which allows the instrument to be used in surveys by a three-stand scheme. Improved models, TheoO20A (Fig.5.l4a) and TheoO20B, have a new unique system of coaxial tangent and clamp screws for simultaneous locking of the vertical and horizontal

axes and a more perfect reading system (Fig. 5.14b). These instruments are intended for the construction of survey nets in mines and on the surface and of reference nets in underground workings. Theodolite TheoO80 (GDR) is a compact optical repeating theodolite with a detachable base for three-stand scheme surveys; it can also be mounted on console holders. Limb graduations have double numbering: one of them being read off when the instrument is mounted in the common upright position and the other when the theodolite is mounted on a console holder in an inverted Dosition.

92

Ch. 5. Horizontal

Surveys

of Underground

Workings

is swinged slightly and if the image of the object again deviates from the cross hairs, the move of foot screws is made more tight by means of tightening nuts. 2. The bubble level of the horizontal circle alidade is adjusted (when required) so that the bubble level axis can be truly perpendicular to the vertical rotation axis of the theodolite. For checking, the bubble level is arranged amid the line of two foot screws of the tribrach and, by rotating these screws in opposite directions, the bubble is moved into the centre. The alidade is then turned through 180°. If the bubble deviates from the mid position, half of its deviation is taken off by operating the foot screws and the other half, by means of the adjusting screws of the Fig. 5.15 View field of reading-off microscope of bubble level. After that the alidade is rotated theodolite, type Theo080 (reads 359 o 28' on through 90° and the bubble is centred by horizontal circle and 96 o 04' on vertical circle} means of the third foot screw. The check is repeated until the required conditions are The field of view of a reading-off microscope satisfied. is illustrated in Fig. 5.15. The instrument is 3. The position of the telescope cross hairs intended for supplementary surveys in underis tested and adjusted. The horizontal line of eyepiece cross hairs must be perpendicular to ground workings. the vertical axis of rotation of the theodolite. For this test, the theodolite is mounted on 5.8. Tests and Adjustments the tripod, and its vertical axis is arranged of Theodolites truly vertical. Then a convenient point is chosen, and its position relative to the horiBefore starting the survey work, theodolites, tripods, and sighting devices are tested zontal line of the eyepiece cross hairs is in order to avoid the influence of probable observed when rotating the instrument stanerrors on the results of angular measure- dards by the horizontal tangent screw. ffthe image (point) deviates from the horizontal ments. 1. The tripod and tribrach are tested for line, it is required to take off the eyepiececap, stability. To test the tripod for stability, the slacken four fastening screws, and turn the theodolite is mounted on it and the vertical eyepiece so as to horizontalize the horizontal axis of the instrument is set truly vertical. The hair. Upon adjustment, the eyepiece is fastentelescope is then sighted on a distinct object, ed again and the cap is screwed into place. and the tripod table is swinged slightly back 4. The collimation error, which can and forth. If the image of the object is then appear if the collimation axis of the telescope noticed to deviate from the telescope cross is not perpendicular to the axis of rotation of hairs, the wing nuts at the tops of the tripod the telescope, is measured and eliminated. legs must be tightened more firmly. For this, telescope is set roughly horizontally After the tripod has been made rigid, the and aimed at a remote object. Readings are stability of the tribrach is tested. The tribrach taken at two positions of the circle: 'face left'

5.9. Centring

of Theodolites

(FLJ and 'face right' (FRJ. Then the clamp screw of the tribrach is loosened, the theodolite is rotated through 180° and locked again by the clamp screw. The telescope is aimed at the same object and two new readings are taken at two positions of the circle: FL2 and FR2. The collimation error can then be calculated by the formula: (FLl

-FRl

:t 1800) + (FL2 -FR2

c=

:t 180°)

4

For correcting the collimation error, the eyepiececap is taken off to open an accessto the adjusting screws of the cross hairs, and the horizontal circle is set at a reading that is determined by the formula: FR = FR2 -c The graticule (cross hairs) is moved horizontally by means of the adjusting screws until the cross is aligned with the image of the object chosen earlier. The check is repeated until the condition is satisfied. The permissible collimation error should not exceed 30". 5. The zero point (zero offset) is tested and adjusted. The zero point in the reading on the vertical circle when the collimation axis of the telescope is truly horizontal and the bubble of the bubble level of the vertical circle alidade is in the zero point. The zero point of the vertical circle must be known and ed for in surveys or be excluded. The zero point value is determined by sighting on one and the same point, preferably closer to the horizon, at two different settings of the circle and in the general casecan be calculated by the formula: ZP=

FL + FR + 180° 2

If the reading is less than 90°, add 360°. For the correction of the zero point, the vertical circle is set at the reading FL-ZP and the cross of the graticule is aligned with the image of the selected point on the object

and Signals

93

by moving the graticule vertically by means of the adjusting screws. The test is repeated if required. When testing and adjusting the zero point, it is essential to observe the position of the level bubble on the horizontal circle alidade; if the bubble is moved aside, it must be centralized by means of the foot screws of tribrach. 6. The compensator is tested. This test is carried out to check whether the vertical circle reads the same when the vertical axis of the instrument deviates within ::t:3'. For this test, a distinct point is chosen and the theodolite is mounted on the tripod so thatone of the foot screws is oriented in the direction of that point. The bubble of the adjusted cylindrical bubble level is brought into the central position so that the main axis of the theodolite is truly vertical. The theodolite is then tilted by 2-3 " i. e. by 4-5 level divisions, towards the selected point by operating the foot screw facing that point. After that the theodolite is levelled by the other two foot screws. With a tilted position of the theodolite, the telescope is sighted on the selected point, and the reading is taken on the vertical circle. The procedure should be repeated with the instrument tilted by 2-3' in the reverse direction, i. e. towards the observer. The difference between the readings taken with the instrument tilted in two opposite directions should be not more than 0.1. Otherwise, the theodolite should be sent to the manufacturer for adjustment. 5.9. Centring of Theodolites and Signals When running a theodolite traverse in underground workings, the instrument is set up successively in the traverse points and, before making angular and linear measurements, should be prepared for operation, ioeo it should be centred and levelled. and its

94

Ch. 5. Horizontal

Surveys

telescope should be prepared for observations. The plumb lines are hung or signals (sighting marks, or targets) are established in the "points to be sighted. Centring is essentially the placing of a theodolite or signals into a position in which their vertical axis is brought into coincidence with the vertical line ing through the centre of a survey mark. Suppose that we have to measure a horizontal angle a = BAC (Fig. 5.l6a). If the theodolite is not centred properly, its vertical axis may turn out to through a point A l' rather than through A. Then, the measured angle will be a1, but not a. The difference L\a = a -a1 is called the error of angular measurementcaused by inaccurate centring of the theodolite, and the horizontal distance AA1 = I is the linear error of theodolite centring. Suppose now that the signals at sighting points B and C have been centred poorly (Fig. 5.16b). In that case, L\a' = a -a2 is the error of the horizontal angle measurement caused by inaccurate centring of the signals, and the horizontal distances between points BB1 and CC1 are the linear errors of signal centring. If the linear errors of theodolite and signal centring occur simultaneously, the total error (a)

A

Fig. 5.16 Deternlination of measurement error of horizontal angle caused by inaccurate centring of (a) theodolite and (b) signals

of Underground

Workings

of measurement of horizontal quite substantial.

angles may be

The root-mean square error in the measurements of horizontal angles caused by inaccurate centring of the theodolite and signals can be determined by the formula: m.

'.'

.=

J- ~2b 2a

2 [l;(a2

+ b~) + lfh(a2 + b2 -2abcosa)] (5.2)

where a and b are the horizontal projections of the side lengths of the measured angle and I,h and Is are the linear errors of theodolite and signal centring. Taking, for instance, that a = 21 m, b = = 28 m, 11= 175°, Is = 0.001 m, and I,h = = 0.002 m, the error of angle 11will be equal to 24". The analysis of formula (5.2) suggests the following conclusions: I. The effect of the signal centring error is independent of the magnitude of the measured angle. 2. The effect of the theodolite centring error depends on the magnitude of the angle and is the highest for angles close to 180°. 3. The effect of the errors of theodolite and signal centring is inversely proportional to the lengths of the sides making the measured angle and increases with the difference in the side lengths. As may be seen, all these factors, which worsen the accuracy of horizontal angle measurements owing to poor centring of theodolite and signals, are typical for the conditions of surveying in underground workings. In that connection, the matter of theodolite and signal centring is of prime importance in mine surveying. Three main methods of centring are used in the mine surveying practice: with a mechanical plummet, with an optical plummet, and automatic centring. In centring with a mechanical plummet, the theodolite is mounted on a tripod or console holder, its vertical axis is set truly vertically

5.9.

(a)

Fig.

5.17

Centring

(b)

Types

of centring

of

Theodolites

(c)

string

and

Signals

(e)

plummets

and the telescope is set into the horizontal position. The string of plummet is ed through the hole of a survey mark and the height of plummet suspension is controlled so that the plummet point is just to touch the top centre of the theodolite. After that the instrument is moved on the platform of the tripod or console holder until the point of the freely hanging plummet is exactly over the top centre of the instrument. Upon making these operations, the continuation of the vertical axis of the theodolite will through the centre of the survey mark if only the top centre of the instrument (with the telescope arranged strictly horizontally) lies in the vertical axis of rotation of the telescope and the plummet point lies in the same vertical line with the plummet string. When plummets are used as signals, the sighting axis of the telescope is aimed at their strings. The following types of mechanical (string) plummets are used in the modern mine surveying practice (Fig. 5.17): (a) a simple centring plummet which has a massive metal body 3 sharpened at the bottom; the sharpened portion ends with a steel point 4; the

plummet is connected with a string 1 by means of a threaded plug 2 at its top; (b) a plummet with a retractable point; (c) and (d) controllable plummets with respectively external or internal pulleys on which the string is wound; and (e) a controllable plummet with an internal reel, which is the most convenient type in operation, since its centring point 6 can be quickly set at the desirable height. On pressing the top portion of a sleeve 1, the plummet string can be freely unwound to the required length. In order to raise or lower the plummet, the operator holds the plummet body 4 by one hand and rotates the sleeve by the other. Depending on the direction of rotation, the string will be either wound onto the reel or unwound from it. To fasten the string to the plummet, the sleeve is taken out upon removing a nut 2, and one end of the string is ed through the slot in the rim of a reel 3 and got made into a knot. The other end of the string should be ed through two side holes and one central hole in the sleeve, after which the plummet can be assembled. At the end of plumbing, the plummet point should be retracted by turning a sleeve 5.

Ch.

5.

Horizontal

Surveys

The surveys in underground workings are carried out with the use of illuminating plummets whose body incorporates, in ad9ition to the string-winding mechanism, also a power source, an electric lamp, and a conical transparent cap. Illuminating plummets are also employed successfully in the orientation of underground workings and check surveys. It is usually warranted by plummet manufacturers that the deviation between the plummet point and the centre of a string hole is not more than 0.5 mm. This can be checked by hanging a plummet and setting up two theodolites at a distance of 5-7 m from it so that the sighting axes of the two instruments, when pointed to the plummet, make an angle of roughly 90°. The telescopesof the two instruments are sighted on the plumb line so that the plumb line and plummet point are within the bisector of cross hairs. If the image of the plummet point in at least one telescope is beyond the bisector, the plummet tested should be repaired or rejected. For more accurate centring, modern theodolites and signals are provided with optical plummets or optical centring devices. The former are built in into an instrument, while the latter are detachable optical plummets and optical centring devices may be either one-sided or two-sided. A one-sided optical plummet permits centring by a vertical collimating ray to be performed either only upwards or only downwards. The scheme of an optical plummet for centring above a surveying mark is shown in Fig. 5.18. By pointing the telescope to the zenith, the theodolite can also be centred under a surveying mark. In the mine surveying practice, when there is no need to fix the intermediate vertexes of theodolite traverses, it is common practice to employ automatic centring of theodolites and signals on tripods or console holders by using a special set of attachments, such as that illustrated in Fig. 5.19.

of

Underground

Workings

3 ~ ~-

Fig. 5.18

Optical

2-mirror;

3-objective;

plummet:

~

I-protective

4-graticule;

glasses;

5-eyepiece

The essenceof the automatic centring of a theodolite and signals consists in that the attachments mentioned make it possible to set up the theodolite in the points where a signal was set up before, and vice versa. This ensures that the vertical axis of the instrument, which es through the centre of a surveying mark, restores automatically its geometrical position when the theodolite and signal setups are interchanged. This interchanging requires no additional centring. Survey with Automatic Centring of Theodolite and Signals. The sequence of survey with automatic centring of theodolite and signals is as follows. Suppose that a checking theodolite traverse is to be run between two groups of fixed mine survey points: A, R, C and D, E, F (Fig. 5.20). To do this, s (bases)(see Fig. 5.19) on tripods are set up in points A and C and centred by means of an optical plummet and the theodolite is set up and centred in a point R. Signals c are then mounted on the bases in the points A and C and the checking angle ARC is measured by

5.9.

Centring

of Theodolites

and

97

Signals

b

A d

9

Fig. 5.19

Set of attachments

to theodolite

T30M

the theodolite in the point B. Then the theodolite and forward signal are interchanged on their bases and the rear signal is set up on a tripod (or console holder) in a point 7 The signal in the point 1 is set into the upright position by means of a level tube on a bracket and, then the angle BCl and the length of a side Cl are measured. The theodolite and forward signal are then interchanged on their bases and the rear signal on the tripod is reset onto a next point to run the traverse to the second group of fixed points D, E, and F where, as in the points A, B and C, the bases are set up by means of an optical plummet or a theodolite. This order of survey is characterized by that the theodolite and signals can be interchanged without intermediate centring, the traverse vertexes between the fixed points are not fixed, and the survey is done by using three stands. For that reason this method is also called the survey with lost points, or survey by a three-stand scheme. 7-1270

for surveying

by three-stand

scheme

A similar survey with lost points and automatic centring of theodolite and signals can also be performed by using console holders instead of tripod stands. This method is usually resorted to in steeply dipping workings or where the mine traffic is intensive. The set of attachments for this method 4

Fig. 5.20 Scheme of theodolite two groups of reference points

traverse between

98

Ch. 5. Horizontal

Surveys

of survey (see Fig. 5.19) contains console holders with adapters (e), centring plates with spherical level tube (a), a clamp (b) for fastening a console holder to wooden or metallic mine s, pin (1), prism attachment (h) for an objective, and a level tube (g). As has been found by experiments, the errors of centring of theodolites and signal~ by various methods are as follows: 1.2-1.5 mm in single centring with string plummets, 0.8-1.0 mm in optical centring, and 0.3-0.8 mm in automatic centring. 5.10.

Measurements of Horizontal

Angles

The operation of measuring a horizontal angle includes centring a theodolite under or over a fixed point in an underground working, sighting on signals, and taking readings on the scales. The sequence of signal sighting and the order of reading on the scales depend on the method of angle measurement employed by a surveyor. In mining workings, left-hand angles along a survey traverse are usually measured by the method of repetitions (reiteration method), method of sets or, less frequently, method of rounds. 5.10.1 .Reiteration

Method

In view of the wide use of repeating theodolites in the mine surveying practice, the method of repetitions (reiteration method) has become very popular in measurements of angles. It consists of the following operations. I. The zero division of the alidade of a horizontal circle is roughly aligned with the zero mark of a limb, after which the latter is unlocked and the hair cross of a telescope is sighted on the rear signal set up in a point B (Table 5.4). The reading 01 is taken on the scale 01 (01 = 0000'.2).

of Underground

Workings

2. The alidade is unlocked and, by rotating the instrument clockwise, the telescope is sighted on the forward signal in a point C to take the reading a2(a2 = 58°23'.5). 3. The telescope is reversed, the limb is unlocked and turned together with the alidade to sight the telescope on the rear signal; no reading is taken. 4. The alidade is unlocked and rotated counter-clockwise to sight the telescope on the forward signal and take the reading a3 (a3 = 116°47'.7). 5. The left-forward angle ~ and its check value ~chare calculated by the formulae: ~ = (a3 -aJ/2 (5.3) ~ch= a2 -al

(5.4)

If the discrepancy between the measured and check angle is more than 1.5 of the instrument accuracy (:!: 1.51),the angle measurement must be repeated. When running theodolite traverses of higher accuracy, the measurements of horizontal angles are repeated more than twice. In that case, in the first position of a circle (say, FL), the limb is moved n times to sight the telescope on the rear signal and the alidade is also moved n times to sight the telescope on the forward signal. Readings are taken only on the first and second sighting, and the check angle is calculated by the formula ~ch= a2 -al. The total value of the angle measured n times will be equal to a3 -al. After that, the telescope is reversed and sighted n times on the rear and forward signal in a different position of the circle. Only one reading, a4' is taken after the last sighting on the forward signal. With n full repetitions, we have: ~ = a4 -a1 + R360°

(5.5)

2n

where R is the number of full revolutions of the alidade around the limb. The number of full revolutions of the

5.10.

Measurements

alidade around the limb can be determined by considering the measured check angle and the number of performed repetitions: R = (2n 13ch + a1 -a4)/360° (5.6) 5.10.2.

Method

of Sets

The measurement of an angle (for instance, CDE, Table 5.5) by the method of sets is carried out in the following sequence. 1. The limb is locked in a position when it roughly reads 00, the telescope is sighted on the rear signal (point C), and the reading a 1 is taken on the horizontal circle and recorded in the field book (01 = 10°07'.5). 2. The alidade is unlocked and the telescope is sighted on the forward signal (point E) to take the reading 02 (02 = 68°31'.0). The measured angle in one position of the circle, i. e. in the first half-set, is 13'= 02 -01 (13'= = 58°23'.5). 3. The limb is turned through 60-90° and locked. The telescope is reversed and sighted again on the rear signal; the reading 03 is recorded in the book (03 = 190°07'.5). 4. The telescope is sighted again on the forward signal to take the reading 04 (04 = = 248°30'.9), and the angle measured in the second position of the circle is calculated: 1311 = 04 -03 (1311 = 58°23'.4). The mean angle calculated by the two half-sets 13m = (13'+ 1311)/2 is taken as the final value (13m= 58°23'.45). In angle measurements by the method of two sets, the sequence of operations is essentially the same, but the limb for the second set is turned initially at a reading close to 90°. 5.10.3.

Angle Measurements Method of Rounds

by

The procedure of angle measurement by the method of rounds consists essentially in the following.

of Horizontal

Angles

99

1. The zero divisions of the limb and alidade are roughly aligned, and the alidade is locked. With the limb unlocked, the telescope is sighted on the initial signal (for instance, point B, Table 5.6) set in the centre of a bench mark, and the reading at is taken and recorded in the book (at = 00003'.0). 2. The alidade is freed (with the limb being fixed) and the telescope is sighted on the signal set in the centre of a bench mark D. In this case,the theodolite is rotated clockwise. The reading a2 is taken and recorded in the book (a2 = 28°08'.1). . 3. The alidade is rota-ted clockwise in the same sequenceand the telescope is sighted on the signal in a point C to take the reading a3 (a3 = 58°26'.7). 4. The observations of the first half-round are finished by sighting the telescope on the signal set in the initial direction B and taking a check reading. This makes it possible to prove that the limb was fixed during the observation of the point (a4 = 00°03'.1). In order to eliminate the instrument error of the theodolite, the same angles between the given directions are then measured at a different setting of the circle (FR). In the second half-round, observations are made in the reverse direction and the alidade is rotated counter-clockwise. The second round is performed in the same sequence, but the limb is initially set at a reading close to 90°. Upon completing the measurements at the second setting of the circle, the collimation error is calculated by the formula: 2c = = FR -FL ::!: 180°; its magnitude is indicative of the accuracy of measurements. After that the mean values of the directions obtained by two measurements are calculated. by the formula: (FL + FR ::!: 180°)/2. The procedure is finished by calculating the corrected directions, i. e. by calculating the mean initial direction from the mean directions found; in our case, the corrected direction is (00°02'..80+ 00°02'.90)/2 = 00~02'.85.

::;Q .: 01 8 = Q ..c ~ .. ~ ." .:, !fJ = 01 8 ~ = "' ~ 01 ~ ..

~ 01 = ~ ~ = ~ ..

~ 00 O ..., ~ E-- 8

>,

1-. ~

...t.s = = ~ ... 8 o ~ ...~ ...> "' = -rnO

8 0 0

~

~ = <

u

I

-

= .~

.

;. 01

~

..."' Q

..~

;..

Q).d 0

o. 8

B

Q Q = ~ ..i::'

Q ~ ~.

~ .~ --~ I£)

01

E--r/JZJ!:.-

3C;~8 ~ ='

00 ~ ... t.s

~

~

. .

.

"5 ~ 00

"' 8';< 000 .J=" ~ 0) " a§ -'" "'.-"' Q.5

., =' ~ I: ~ ~

~.~

~

..1 ~

]

.

~ "E:

1:1. I o

.=: ~

e "'-

1~.5

,"].,-5 '00 ., ~

~ ~ .0 ~

.: O '.: '" ~

= ~ 0

"0

i' ~ = ~ = -= .. Q; e '-'

'tJ = Q; e ~ = "' ~ Q; ~ ..

~ O 00

~ s +"' "' = =

8 0 "' r-I

~ 00 > G) ...+"' =' "'

s ~ e +"' "' = -000

; = ~ = <

";) > .£

= ~

~ Q; = ~ ~

= ~ =

~ .-

..

~ .. -~

~

~ ..Q;

P.8 >.

u ~

.-~ ~ II")

Q; ..: .. ..~ ~ o VJVJ

Q; .-Q; ~

Q; -> .c ~ E-

~

"0 ",,~ ","0 '".~ ~""'",,,

"' = .0 ~

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,

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..,

~ 0 ..,

~ .c

I

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Ir) r--v '0 -0 Nr'"\ oN r'"\OO Ir)

1'"10r-.:o 0... 000 O\~ -<""1

o o N

1 0 \Q

0 ""' 0

.

~ ""' N 00 Ir)

Ir\ ..; N Ino r..:...; 0

00 00 o

~ 'r\

00 N on

I

or\ or\ -

~~ ...,...,

~

IDN OOID

~

000 --0

\,)

~

r-ID

~ ...,

'(ij' -= = = e

'Q -g .c ~ ,§, "' .. = .. e .. .. = "' " ..

~ .. ~ = <

'; = = N .~

8"

..

011

~ O M

..

~ -= =

011

o ~

I

e

=

"8

e

-" "' = -VJO

I:: ~

ci)

=

= .,s ;:I 0 ..0

'- "'

"Q)

~ = =

~

u>-o "' ..\r\ 0. I:: ~

-=

~

>-~

>

Ir)

..~~.c ->-~ ...~ " ;:I .-" Eo-(/J~-

-13 .., ~

"g ~ ~ 0 ~ .;;; I: ~ O .!= U"O

;1 N

~ 'X>

+1 .-1 "" I ~ "" II " N

~ ~

i

"' c '5 ~

~.5 o c ~.,g

-1o.r;M OON 00000 ON"'

0"'00 ~~\0~ Nr.:IQN ooNo

000000 ONIr)O

"""'N~ 0000

0000 0000 I I

10 00"' Nr-:IQN OONO 000000 000...'00 -~~-

o-r-'.;00,cj'.; OONO

000000 ONIr)O

~~v~

~

Ir\

I

I

r--

~

102

Ch. 5. Horizontal

Surveys

of Underground

Workings

III

(b) III

,

--

/

"' / /

Fig. 5.21

Measurement

of horizontal

angle by eccentric

The measurements of horizontal angles in underground workings with the angles of dip more than 300 are made only by the method of sets under the provision of the following additional conditions: I. If a repeating theodolite is employed, its limb must be locked for the entire time of measurements. 2. The theodolite for measuring horizontal angles must be provided with a striding level and permit plumbing of its vertical axis of rotation before each set. 3. The alidade of the theodolite should always be rotated in one direction only. 5.10.4.

Measurements of Horizontal Angles by Means of Eccentric- Telescope Theodolites

telescope

is shown in Fig. 5.210 and with the circle at left, in Fig. 5.21b. In order to measure the angle between the directions II-I and 1I-111, for instance, with the circle at right, the telescope is sighted successively on signals I and III. In that case, the horizontal axis of rotation of the telescope moves from position II-I into 1I-2, i.e. its setting is changed by an angle 13" and therefore, the angle 13,will be measured instead of 13.Similarly, with the circle at left, the angle 13! will be measured instead of 13. As may be seen in Fig. 5.21, the exterior angles

Rp 11'-" ,

where
,

"

" ~

!.0.0

r

Lu ~'a, L~ ," R 17' Rdr

L

p

~~/&'/~~~

"'-' ~

./ ~

~

Fig. 9.19 Inclination angles of hoisting ropes

drum and pulley;
d..

L where hv is the height of a hoisting vessel; hi is the height of overlifting; hp is the elevation of the top pulley axis over the bottom pulley axis; and Rp is the pulley radius. The hoisting axis of a vertical shaft is the straight line that es through the point midway between the two vertical hoisting ropes perpendicular to the axis of the main shaft of a hoisting machine. The hoisting centre of a single-rope hoist is the point that <;:oincideswith the projection of the rope axis onto the horizontal plane; for a double-rope hoist, this is the point of intersection of the hoisting axis with the straight line ing through the axes of the two vertical hoisting ropes. The centre of the shaft of a hoisting machine is a point on the axis of the main shaft midway between the internal edges of the rims of a drum (for single-drum machines) or midway between the internal edges of the rims of drums (for two-drum machines). The axial plane of a guide pulley is the straight line that esperpendicular to the axis of a pulley shaft midway between the internal faces of pulley rims. The inclination angles of hoisting ropes are the angles

where H p is the height of the pulley axis above the zero stage; Hdr is the height of the drum axis above that stage; and L is the horizontal projection of the line connecting the axes of the pulley and drum. The A

A(D - Rdr -Rp 'I Loc

where Rdr and Rp are respectively the radii of the drum and pulley of the hoisting machine and Loc is the distance between the centres of the drum and pulley (0 and C). The length of a rope string is the distance between the point of run-off of the rope from the drum and the point of run-on of the rope on the guide pulley. It is distinguished between the string of an upper rope, Lu, and that of a lower one, L (see Fig. 9.19). Among various types of hoisting machines, those with cylindrical drums are the most popular, that is why the characteristics of rope coiling will be discussed for this type of machine. The distance between the internal faces of the rims of a drum is called the construction width and denoted Ldr. Various portions of the construction width of a drum serve different purposes and accordingly the following zones are distinguished (Fig. 9.20).

206

Ch. 9. Surveying

in Mine

Construction

cated: hemp =

Ldr

( H+ ~

30 +

n

)

(d

e)

The zone of working coils of a width hw which depends on the total hoisting height and can be determined by the formula:

h=cw

H

(d + e) 1tDdr

where H is the total hoisting height; d is the rope diameter; D dr is the drum diameter; and e is the spacing between the adjacent coils of a rope. The zone of reserve coils, br, which is needed to take on the additional length of a rope. Its width can be found by the formula: 30 b. = -=--(d + e) 1tl}dr where 30 is the additional length of a rope, ill, required for strength tests. The zone of friction coils, hfr , which is provided for stronger holding of the rope on the drum. This width is usually determined by three or five rope coils, i. e. hfr = n(d + e) where n = 3-5. The empty portion of a drum, hemp,is the difference between the construction width of a drum Ldr and the SUm of the zones indi-

where a is the distance from the hoisting axis to the pulley plane at the pulley axis; bl and b2 are the distances from the hoisting axis respectively to the farther and closer end of the working portion of a drum; and L is the vertical distance between the centre lines of the drum and pulley of the hoisting machine. In order to make the fleet angles on a pulley equal to each other (131 = 13u)'the axial plane of the pulley is oriented onto the centre of the working portion of the hoist drum. In cases when the axial plane of a pulley is arranged parallel to the axis of a mine shaft, the fleet angles of the rope on a pulley and drum ar~ equal to each other (al = 131, au = 13u).If the axial plane of a pulley is not parallel to the hoisting axis, the fleet angles

208

Ch. 9. Surveying in Mine Construction takes place when a,-au 1'=

2 cos q>

Substituting the expressions for a, and au into this formula, we obtain the condition that makes it possible to find in each particular case the magnitude a2 -al , i. e. the magnitude by which a pulley should be turned so that its axial plane will be oriented onto the centre of the working portion of a drum: +b2

- 2a

2Lcos

D,

Geometrical elements of a multi-rope hoist. The scheme of the most popular four-rope hoist with pulleys which deflect one system of ropes is shown in Fig. 9.22. The main geometrical elements of this hoist are as follows: the axes of hoisting ropes of a non-deflected rope system (2); the axes of intermediate rope strings between the drive pulleys and guide pulleys (9); the axes of hoisting ropes of a deflected rope system (6); the mean points of suspension devices (4, 5); the mean point of rope run-off from guide pulleys (3); the mean point of rope run-off from drive pulleys (1); the axis of the non-deflected rope system (8) which is a straight line connecting the mean run-off point and the mean point of a suspended balancing device; the axis of the on the pulley can be found by the formulae: deflected rope system (7) -a straight line connecting the mean run-off points and the 13,= a, -ycos , 13u= au + ycos mean point of a suspended non-balanced where y = [(at -a2)/Dp] p' is the horizontal device; the hoisting axis v-v which is a angle of the turn of a pulley relative to the horizontal line ing perpendicular to the hoisting axis; at and a2 are the distances from main shaft axis through the mean run-off the hoisting axis to the pulley plane at the point on drive pulleys; the vertical axes of the ends of the horizontal diameter of a pulley; hoisting compartments of a tower head-frais the angle of inclination of a hoisting rope; me; and the angles of bending of hoisting and D p is the pulley diameter. ropes by guide pulleys. For normal operation of pulleys, which In multi-rope hoisting machines, it is disprevents one-sided wear, the fleet angles on a tinguished between the following fleet angles: pulley must be equal to each other, which (a) the fleet angles of descending ropes on

(c)

10

3

\

9

I~-

L.u

~-

-

J1~

-/10 ~ 11 Fig. 9.23 Geometrical elements and parameters of multi-rope hoisting plant: (a) and (6) vertical projections; (c) plan view; 1-drum of drive pulleys; 2, 3-mean run-off points of ropes on drive and guide pulleys; 4- guide pulleys; 5 -level of guide pulleys; 6- numbers of ropes; 7- bunton; 8- hoisting vesselclip; 9-conductor; 10-mean point of suspension device (clip); 11- hoisting vessel; l-length of intermediate rope string; h-elevation of main shaft axis above guide pulley shaft axis; hi, hl -elevation of main shaft axis and guide pulley shaft axis above guide pulley stage level; h3' h4 -elevation of main shaft axis and guide pulley shaft axis above mean points of suspension devices; R"p. Rgp- radii of drive and guide pulleys 14-1270

j

210

Ch. 9. Surveying in Mine Construction

drive pulleys, ai, Fig. 9.23 (an angle formed by the axis of a rope with the plane of a drive pulley); (b) the fleet angles of descending ropes on guide pulleys, Pi (an angle between the axis of a descending rope and the plane of a guide pulley); and (c) the fleet angles of intermediate rope strings on drive pulleys (~J and guide pulleys ('1'J. In addition to fleet angles, of essential importance are also the angles of deviation from the vertical axis of symmetry of the system of ropes and the angle of (wrapping angle) of a rope on a guide pulley, 11 (see Fig. 9.23). The elevated fleet angles of ropes are the main cause of quick wear of a pulley lining, while the deviation of a rope system from the vertical may cause increased horizontal loads exerted by hoisting vesselson the shaft equipment. The fleet angles of ropes on drive and guide pulleys of multi-rope hoisting machines must not exceed 30-40'. The control of the relation between the main geometrical elements of hoisting machines of this type consists essentially in observing the following requirements: (a) the axes of the main shaft and guide pulley shaft should be horizontal and parallel to one' another; (b) the axes of main hoisting ropes should be perfectly vertical; (c) the drive and guide pulleys of a rope string should lie in the same vertical plane; (d) the straight line connecting the mean run-off point of a rope and the mean point of a suspension device should lie on the vertical axis of a hoisting compartment; (e) drive and guide pulleys should have the same diameters corresponding to the design specifications; and (1) the angles of deflection of ropes by guide pulleys should be within the limits of 8-15°. The experience of operation of multi-rope hoists has demonstrated that the design dimensions of these machines should be observed with a high degree of accuracy, since their deviations may influence substantially the operating conditions of a hoisting ma-

chine, lead to uneven wear of a pulley lining, and cause uneven loads on ropes and elevated forces acting .on conductors. The main causes which may lead to the distortions in the relation between the geometrical elements and deviations of main ropes from the vertical are as follows: (a) inaccurate assembly of a hoisting machine and equipment; (b) wear of a pulley lining, and (c) displacement of a hoisting machine or equipment due to underworking a tower head-frame or mine shaft. 9.3.5.

Survey Work During of Hoisting Plants

Mounting

Survey work for mounting a hoisting plant consists in transferring the hoisting axis and the main shaft axis into the hoisting plant building and laying out the foundation for the hoisting machine and its elements. The layout work is started by transferring into nature the point of intersection of the axis of the main shaft and the axis of the hoist shaft. Upon erecting the walls of the hoisting machine room to a height of 1-1.5 m above the ground, the axis of the main shaft and the axis of the hoisting machine shaft are transferred by means of a theodolite inside the building and fixed by brackets on the inner walls. Mter erecting the building walls to the full height, a second row of brackets (mounting brackets) is built in at a height somewhat below the ceiling floor level. The axial points are transferred onto these brackets from the lower ones by a theodolite or plumb bobs. The hoisting axis and the machine shaft axis are laid out twice. The mean direction angle of the main shaft should differ from the design value by not more than 2', and the angle between the two fixed perpendicular axes should differ from a right angle by not more than 1'. The distance from the centre of the mine shaft to the machine shaft should differ from the design value by not more than 100 mm, and the side displacement of the

9.3. Surveying in Construction of Mine Hoists

point of intersection of the hoisting axis and machine shaft axis, by not more than 50 mill. The permissible deviation of the machine shaft axis from the horizontal position is established by the specifications for hoisting machine assembly. Mter laying the ing frame of a hoist into its place, it is checked for horizontality and correct position relative to the hoisting axis and the main shaft axis of the machine. The position of the frame along the height is checked by levelling the corner points of the frame in plan relative to the axes by means of plumb bobs. The deviation of the frame from its design position should not exceed 10 mill in plan and 100 mill vertically. The highest difference of elevations of the corner points of the frame should be not more than 15 mm. The arrangement of the main shaft bearings is checked along the height by levelling the lower points of their internal surface and in the horizontal plane, by means of plumb bobs hung from a cord stretched between the axial brackets of the main shaft of the hoisting machine. The deviations of bearings in plan and vertically should not exceed 1-2 mill. The actual position of the shaft of the hoisting machine is checked by the same method as the position of bearings. Mter the completion of the machine assembly, the position of the drum relative to the hoisting axis is checked by hanging two plumb bobs and measuring the distances from the plumb bob lines to the drum rims. 9.3.6.

14.

traverse A-I-2-3 (Fig. 9.24) is run from the layout axis of the main shaft which is taken as the initial direction. The point 4 of a traverse is fixed approximately on the hoisting axis near the zero stage. The angle 2-3-1 is laid up at a point 3 (from the side 3-2), which is calculated so that the direction 3-1 is perpendicular to the axis of the machine shaft. This direction is transferred onto the pulley stage and fixed by a wire I-II. At the pulley stage, the distances a1, a'1' a2 and a~ from the wire I-II to the external edges of pulley rims at the ends of a horizontal diameter are then measured. The distance 1 between the external faces of the pulley rims is also measured. In the machine room building, there are measured the distance between the internal faces of drum rims ho, the width of empty portion of the drum h and h', the width of the working portion hw and h;., the +x

I

'~~ ""\ ~ ~,

~

SItB ~~

Survey Work for Checking the Geometrical Elements of a Single- Rope Hoisting Plant

After the assembly of a hoisting plant, it is required to check the horizontality of the axes of machine shafts and drive pulleys, the positions of the axes of hoisting ropes relative to conductors at the level of the zero stage, and the fleet angles of hoisting ropes on drums and pulleys. For this purpose, a theodolite

211

/.

2

/

Fig. 9.24 Theodolite traverse for checking of relation between geometrical elements of hoisting plant

212


total width of the zone of friction coils and reserve coils (bfr + br) and (bfr + b~)for twodrum machines; for single-drum and bicylindrical machines, it is required to measure the total width of the empty portion and of the zones of friction coils and reserve coils (b + bfr + br) and (b' + bfr + b~)and the total width of the drum, B. Taking the system of coordinates with the axis of machine shaft being the y-axis and the axis of symmetry of the machine, the x-axis, it is now possible to calculate the coordinates of theodolite traverse points and of the axes of ropes and conductors. For each rope, there are determined the maximum exterior (a.x) and interior (ain) fleet angles on the drum of the hoisting machine: (a) for a hoisting plant with two cylindrical drums and pulleys: b.x -a, a -bin , a.x= p, ain=-p L L (b) for a hoist with one cylindrical or bicylindrical drum: b.x -a, bin + a , Uin = u"x = .p -:--p 1 L

The distances a and a' for hoisting machines of the first and second type are found by the formulae: a = 0.5(a1 + a2) + 0.5/ :t c a' = 0.5(a'1+ a~) + 0.5/ :t c where c is the distance between the transferred I-II direction and Ox axis, which is equal to the ordinate of point I. For hoisting machines of the third type, the distances a and a' are determined by the formulae: a =10.5(a1+a2)+0.5/-cl a' = 10.5(d1+ a~) + 0.5/-

cI

The inclined distance L (of a rope string) can be found from the expression

L=~ where Lo = x.. -D J2 (here x.. is the abscissa of a rope in the adopted system of coordinates and D p is the pulley diameter); Ah is the height difference of the pulley axis above that of the machine shaft. Since the axis of a pulley may turn out to be unparallel to the machine shaft axis, the fleet angles on the pulley may respectively differ from those on the drum. For pulleys, where p' = 3440'; hexand hin are the distances we determine the two maximum fleet angles from the axis Ox to the rope on the drum in of ropes: an exterior angle ~ex and interior its extreme (exterior or interior) positions; a is the distance from the axis Ox to the axial angle ~in' by the formulae: plane of the pulley; and L is the inclined ~ex= a ex -'Y cos

olstlng

axis

tan

for single-drum and cylindrical machines (see Fig. 9.21h and c) hex= O.5B -hfr h,- = 0.5B -(h'

+ h: + h'..-)

,

y

=

~

p

an

.

lS

t h

e


9.3.7.

Survey Work for Checking the Relation Between the Geometrical Elements of a Multi-Rope Hoisting Plant

Surveying a multi-rope hoisting plant is carried out in order to determine the angles of deviation of the axes of rope systems from the vertical in projections onto the axes x and y (ex, ey, mx' and my),fleet angles of the main and intermediate ropes on drive and guide pulleys (a, ~,

Fig.

9.25

Determining

radii

of drive

pulleys

213

One of the probable methods for determining the radii of drive pulleys consists in the following. A line parallel to the main shaft axis is fixed in the machine room, after which the distances from that line to hoisting ropes are measured. The point A is fixed on the floor of the machine room (Fig. 9.25). A theodolite is set up on that point and sighted roughly along the rope line (direction AaIl). The readings aI and all are taken on two staffs set up in points I and II horizontally and tangentially to the machine shaft. The distances SI and SII from the point A to staffs I and II are then measured. The shaft is measured circumferentially in the points I and II (CI and CII) and its radii are calculated by the formulae rI = cJ21t and rIl = cIJ21t These radii and the measured values aI and all make it possible to take readings on the staffs with the theodolite telescope sighted parallel to the main shaft axis: sIlaI -sI(aIl + rIl -rJ bI=

SII-SI


214

SIl(aI + rI -rIJ

-sIall

bll=

SII- SI The vertical hair of the telescope is sighted at the reading bll of a staff, provided that the sighting line esthrough the reading bI.1f it turns out that (bll + rll) -(bI + rJ is less than 0.5 mm, the direction parallel to the main shaft axis is fixed on a bracket or plate (point B) concreted in the wall of the machine room. Mter that, the telescope is sighted at the point B and the readings 15,16,17,and 18 are taken, with an accuracy to 1 mm, on a horizontal staff set successively to ropes 5, 6, 7, and 8 in points of their run-off from pulleys. The radii of drive pulleys are calculated by the formulae: R5 = bll + rll -(b5 + rr) R6 = bll + rll -(b6 + rr) R7 = bll + rll -(b7 + r r) R8 = bll + rll -(b8 + rr) where r r is the radius of the rope. Fixation of auxiliary axes on the measuring level and determination of coordinates of reference points. The points which fix auxiliary axes are called referencepoints. They are laid off on a cross-piece below the machine room where the ropes descending into the mine shaft are easily accessible. The hoisting vessel is sunk into the lowermost position, and a staff is laid on the m~asuring level to the non-deflected ropes (5, 6, 7, 8, see Fig. 9.26). The shortest distances from the staff to plumb bobs 5 and 8 are then measured. Then, using the calculated radii of drive pulleys, the distances from the main shaft axis to the staff axis are calculated. The staff is then placed in a position so that its axis can be parallel to the main shaft axis, and this direction is fixed by points C and D. Using the method of corner sections, points A and B are marked from these points. They determine the direction parallel to the line of deflected ropes (I, 2, 3 4). Non-parallelity

between AB and CD should be not more than 10'. The coordinates of points A, B, C, and D are determined by ordinate surveying of non-deflected ropes, with the hoisting vessel in the lowermost position, and by measuring the sides and diagonals of rectangle ABCD. The distances from the rope axes to the staff axis and the staff readings corresponding to the projections of the rope axes onto the staff are determined in the following manner. The staff is fixed on points C and D. After an extreme rope, say 5, has dampened, an angle is placed to it (Fig. 9.27a), and an ordinatometer is placed to the staff and moved to the angle. The reading /51is taken by means of a rule against the edge of the angle and the reading! 51is taken on the staff against the ordinatometer edge. The angle is turned into another position (Fig. 9.27b) and new readings 15II and !5II are taken. Similarly, the readings 151II,15IV'!51II'and!5lV are taken in a third and fourth position of the angle (Fig. 9.27c and d). The positions of other ropes are determined in a similar way. The readings are reduced to the staff axis


If aCD::!:90° < 10', then Xc = Xr5 and YC= = v -f 5' where v is the staff reading corresponding to the centre of a hole for the fixation of the staff in the point C (see Fig. 9.27). The angles of rectangle ABCD are found

and rope axes by the formulae: liI +

lill

+

2d -lillI

-liIv

'=k+ 4

1; =

J;I

+ J;II

+J;III

+ J;IV

4

215

where i is the number of a rope; k is the distance from the staff axis to the beginning of the ordinatometer scale; and d is the length of the ordinatometer scale. The values of abscissaeon the staff can be found from the expressions: x r5 = -R 5 + 15' x r6 = -R 6 + 16 --R + 1 --R + 1 Xr7 -7 7' Xr8 -8 8

by solving the triangles into which the rectangle is divided by diagonals AD and CB. Taking the coordinates of the point C as the initial ones and knowing the direction angle aCD' it is possible to determine the coordinates of points A, B, and D. Determination of the angle of turning of guide pulley shaft axis relative to the main .. shaft axis. In order to determIne the angle &,a staff is fixed on points A and B laid up

where R is the radius of a drive pulley. The direction angle ofa side CD (staff axis) can be found by the formula: (x -x) r5 r8 p' aCD = 90° + .

parallel to the line of deflected ropes (Fig. 9.28). Two plumb bobs 01 and O2 are hung at one end of the shaft in a point IV, and a metal rule is laid below them perpendicular to a staff AB. A series of readings n1, n2' n3'

f8 -f5 The

coordinates

calculated

x,

Xc = Xr5 + (V -f5)tan(aCD Yc = v -f5

y

of

a point

by the formulae:

+ 15tan(acD

-90°) -90°)

C

are

n4' etc., and m1, m2, m3, m4, etc. are taken under the centres of plumb bobs, and their mean values are found (n and m). The distance CIVfrom the metal rule to the axis of the staff AB is measured, after which the distance from the shaft axis to the staff axis AB is

216

Ch. 9. Surveying

in Mine

Construction

Staff

Fig. 9.28

Determining

angle of turning

of guide pulley

shaft axis relative

AHI-II

to main shaft axis

+ Arl-ll

°II-

p' SI

where Arl-Il is the difference of radii of the shaft in the measured sections (in points I and II) and SI-II is the distance between points I and II. The angle of inclination of the axis of guide pulley shaft, OIV-III is determined by a similar formula. Determination of the coordinates of rope axes on the measuring level. The coordinates of ropes in two extreme (upper- and lowermost) positions of hoisting vesselsare needed (dIv + d;v) -(dIll + d;lI)0' + (a.D -900) E= for determining the angles of their deviation. 2s The coordinates of plumb bobs are deterwhere s is the distance between points III and mined from reference points CD and AB on IV. the measuring level (see Fig. 9,26) by means Determination of the angles of inclination of of a staff-type coordinatometer. the axes of the main shaft and guide puUey With the hoisting vessel in the lowermost shaft. These angles can be determined with position, we determine the coordinates of the the aid of hydrostatic levels by measuring the axes of non-deflected ropes (Xi' Y;) and those height difference L1Hbetween the end points of of deflected ropes (xr, Yr). Similar measurethe axis of a shaft. The inclination angle of the ments are made with the hoisting vessel in main shaft axis is calculated by the formula: the uppermost position (respectively x;, Y;

The rule is displaced through several centimetres, and a new distance d;v is determined, which should differ from the fornler by not more than 2 mill. Similarly, two distances from the end III of the shaft of guide pulleys to the staff axis AB are determined (dIll and d{lI). The turning angle E is calculated by the formula:


217

measurements; Yr and Y~are the ordinates of the axes of deflected ropes respectively in the lowermost and uppermost positions of a hoisting vessel; Xr and X~are the abscissaeof the axes of these ropes; h2 is the elevation of the axis of the guide pulley shaft above the measuring level; h4 is the elevation of the axis of the guide pulley shaft above the adjacent point of a suspension device; and R9,dand Rg is the design radius and actual radius of guide pulleys at measurements. Thefleet angles ofmain ropes can be found by the formulae: on drive pulleys: a = ey + 8 + A., on guide pulleys: ~ = my + 8' + Ar where 8 and 8' are the inclination angles of the main shaft axis and guide pulley axis and Ai and Ar are the corrections for the position of balancing devices, which can be determined by the formula:

where n is the number of ropes in a system; Yi and Y; are the ordinates of the axes of non-deflected ropes respectively in the lowermost and uppermost positions of a hoisting vessel; hi is the elevation of the main shaft axis above the measuring level; xi and x; are the abscissae of the axes of these ropes; h3 is the elevation of the main shaft axis above the mid point of a suspension device; Rdr,dis the design radius of a drive pulley; Rdr is the actual radius of a drive pulley at

s -s. A=---2 h where s is the distance from the system axis to the axis of a rope at the level of balancing devices; Si is the distance from the system axis to the axis of a rope in a run-off point; and h is taken equal to h3 for determining Ai and equal to h4 for determining Ar. Thefleet angles of intermediate rope strings can be found by the formulae: on drive pulleys: t1.y" .

218


11is the wrapping angle of a rope on a guide pulley; E is the angle of turning of the axis of the guide pulley shaft relative to the main shaft axis; ° and 0' are the angles of inclination of the axes of the main shaft and guide pulley shaft; and 1 is the length of an intermediate rope string: 1 = [h -(Rg + xr) tan 11] where h is the height difference between the axis of the main shaft and that of the guide pulley shaft and Xr is the abscissa of the axis of a deflected rope. The permissible values for the indicated angles are as follows: Ox,Oy,rox and roy not more than 0°15'; angle of inclination of the main shaft axis, 0, not more than 0°05'; angle of inclination of the axis of the guide pulley shaft relative to the direction of the main shaft axis, not more than 0°45'; fleet angles a and ~, not more than 1030' and those for intermediate strings (

dimensions of the shaft, the arrangement of equipment and hoisting vessels, the line of vertical section along which records are being made, and conventional symbols of rocks and lining materials. The second page contains data on the course of shaft sinking. On the third and subsequent pages, a vertical section of the shaft on a scale 1/100 and sketches of shaft elements are drawn. Mine surveying work during the sinking of a shaft can be divided into two periods: (I) initial period during which the shaft is provided with mining (heading) equipment and the shaft collar is constructed and (2) shaft sinking proper. 9.4.1 .Survey Work During the Initial Period of Shaft Sinking

The survey work at this stage consists in transferring the axes of temporary buildings and structures into nature, which is required for arranging a layout network and marking 9.4. Survey Work During Sinking the axes of a shaft according to the dimenof Vertical Shafts sions indicated on the general layout and on The construction of mine shafts include.s the drawings of the arrangement of mining sinking a shaft and the arrangement of a equipment. During the mounting of hoisting lining and equipment. The main object of machines, special attention should be given mine surveying service in the construction of to checking the arrangement of the hoist mine shafts is to ensure the design position of frame relative to the predetermined hoisting the shaft and its elements. To achieve this, the axis and machine shaft (drum) axis, as wen as mine surveyor has to perform the following to correct arrangement of the shaft of the procedures: to transfer the axes of hoisting mine hoist. The deviation of the hoist frame plants into the driven shaft; to assign the from the hoisting axis should not exceed design direction to shaft sinking; to transfer 50 mm; the deviation of the elevation marks and mark the layout net for the assembly of of frame corners from the design level should hoisting machines; to make check measure- be not more than 300 mm, and the elevation ments in the shaft; and to layout shaft marks of corners should differ from one workings and chambers. another by not more than 15 mm. The deAll mine surveying measurements are re- viation of the hoist shaft axis from the axis of corded in a which is the main docu- a layout network should be not more than 2', ment reflecting the actual state of the const- the height difference on one end of the shaft ruction of a shaft (Fig. 9.29). The first page of above the other being not more than 0.001 of the gives the design section of the the shaft length. shaft on a scale 1/50 and the principal The sinking frame should be mounted

9.4. Survey

Work

During

properly relative to the shaft axis; the displacement of the pulley stage in the horizontal plane from the design position should be not more than 60 mm. The layout of the pit for the shaft collar, construction of a cap, and the arrangement of

Sinking

of Vertical

Shafts

Intermediate shoe at -25.5 m

219

a zero frame are carried out relative to the axial lines of the shaft. The displacement of the zero frame axes relative to the design position should not exceed 5 mm, the deviation of the elevation marks of the frame from the design position should not exceed 50 mm,

220


and the difference of elevation marks of the points of the unloading bedframe should not exceed 5 mm. Since the zero frame defines in nature the contour of the shaft cross section, its dimensions and shape should correspond strictly to the design cross section of the shaft. The centre of the shaft is fixed on the zero frame, and the directions of the shaft axes are indicated by marks. The positions of the shaft centre and axial marks are determined twice by independent measurements; the discrepancy between the measurements should be not more than 5mm. The directions of the shaft axes are then transferred from the zero frame into the shaft mouth and fIXed by marks on brackets built in at a distance of 50-100 mm from the walls of the shaft lining. Elevation marks are transferred onto the axial brackets. The displacement of the marks from the axial line should not exceed 2 mm. If upon sinking the shaft mouth to the design level it turns out tpat the actual geological section corresponds well to that designed, permission is given to make the first circular cut for a foundation CUl;b. Otherwise, the problem should be coordinated with the designer. Upon sinking the shaft to the first foundation curb, the position of the shaft along the depth and in the horizontal plane is checked by taping the vertical distances and the distances from the zero frame to the cut floor. The position of the shuttering for the foundation curb is checked in the vertical and horizontal plane by measuring the radii from a temporary central plumb bob to the exterior surface of the shuttering, and the distances from the frame to curve pieces. Upon the construction of the shaft lining, the zero frame is replaced by the main heading frame which is placed .onto the permanent lining of the shaft mouth and oriented properly relative to the centre and axes of the shaft (Fig. 9.30). Deviations above 20 mm

Fig. 9.30 Main heading frame: l-opening for bucket; 2- rescue ladder; 3- ventilation column; 4- concrete pipeline age; 5- compressed air column; 6-central plumb bob

are not allowed. The centre of the shaft is transferred instrumentally from the axial points onto the heading frame, and the guide pulley of the central plumb bob is fixed so that the plumb bob line is not displaced from the shaft centre by more than 5 mm. The survey control of shaft sinking is performed from the central plumb bob and side plumb bobs suspended from the main heading frame. 9.4.2.

Survey Work During Sinking a M ine Shaft

In shaft sinking by the conventional drilling-and-blasting method, the survey work consists in checking the positions of vertical directions, determining the scope of the mining work performed, locating the places and dimensions of rock inrush and backfilling behind the lining, and checking the position of travelling forms and the dimensions of the shaft section and vertical walls of a lining. For the horizontal and vertical control of shaft sinking, there is formed a geometrical basis as a system of plumb bobs, light

5. Survey

Work

for Arranging

indicators or projection meters. Plumb bobs are mostly employed for the purpose. Their number and arrangement depend on the cross-sectional shape of the shaft and the arrangement of mining and hoisting equipment in it. For instance, a single central plumb bob is employed in shafts of a circular cross section, four plumb bobs hung at a distane of 20-30 cm from the shaft walls, in shafts of a rectangular cross section. In shafts of an oval cross section, two plumb bobs are suspended near the walls at each axis of an ellipse. The positions of plumb bobs during sinking a shaft should be checked at least once a month. The deviations of vertical directions from the design values are checked by making measurements from the axial points fixed in the shaft mouth or on the main heading frame. These measurements can be made by using plumb bobs, light indicators or projection meters. In order to minimize errors, the cables of projection meters should be fixed in every 300 or 400 m. The error in the position of fixation points of light indicators relative to the previous level should not exceed 15 mill. The state of shaft walls is controlled by measuring the radii from the central plumb bob to walls in vertical intervals of 3-4 m. The measured results are used to calculate the actual cross-sectional area of the shaft which should not differ from the design value by more than 4-10% for shafts up to 20 m2 in cross-sectional area, by 3-8% for those 20-40 m2 in area, and by 2-5% for those above 40 m2 in area. The permanent lining of vertical shafts is constructed by means of travelling forms which are placed into the working positions relative to the central plumb bob. The position of the travelling forms and shaft walls should be checked by the mine surveyor at least after every three or four travel cycles. The correct position of the travelling forms relative to the central plumb bob is checked

of Shaft

Equipment

221

at least in eight points around the periphery of the forms. The vertical axis of the forms should not deviate from the mean position of the plumb bob by more than 20 mm. The vertical position of the forms is checked by hydrostatic level with an accuracy not worse than 10 mm. The errors of measurement of distances from the central plumb bob to the forms of a shaft lining should not exceed 10 mm. For cast-in-situ concrete and reinforced-concrete linings, the deviations of radial distances from the centre should be not more than 50 mm. A concrete-tubbing lining is built from the top downwards, tubbings (crib seats) being placed after every 20-24 m. They are placed in the presence of the mine surveyor who checks that the distances from the central plumb bob to the internal faces of tubbings differ by not more than 10 mm from the design value. All placed tubbing crib seats and each tenth ordinary tubbing should be controlled by mine surveying. The plan position of a tubbing ring is controlled by measuring the distances from the central plumb bob to selected points at tubbing joirits. Vertical control is effected upon mounting 6-8 rings. If it turns out that the deviation of a tubbing column from the vertical is more tban 30 mm, the lining should be corrected. 9.5.

Survey Work for of Shaft Equipment

Arranging

The main task of the mine surveyor during the arrangement of shaft equipment is to control that buntons and conductors are mounted strictly in their design positions. The equipment of a mine shaft is a complex of structures and elements which ensure correct motion of hoisting vessels.The main elements of equipment are conductors and buntons; the latter are divided into the main and auxiliary ones depending on their position in the shaft. The main buntons are

222


built in into the shaft lining at both ends, whereas the auxiliary ones are either fastened between the main buntons or attached at one end to a main bunton and built in at the other end into the lining. The main bunton arranged in the centre of a shaft or near it is called the central bunton. The combination of main and auxiliary buntons located in the same horizontal plane is called a bunton stage. The distance between adjacent bunton stages is called the pitch of equipment. Conductors (of the rigid or rope type) are fastened to buntons. The arrangement of equipment in a shaft may be done by a consecutive or combined scheme. In the former case, first all buntons are mounted to the entire depth of the shaft, after which conductors are fastened to them. In the latter case, conductors are suspended upon mounting three or four bunton stages.

(a)

(b)

The survey work during the arrangement of the equipment of a vertical shaft includes three stages: (I) the control of preparatory work and the arrangement of hoisting and mining equipment; (2) the control of the arrangement of buntons and suspension of conductors; and (3) the final control of the accuracy of mounting the equipment by making the profile survey of conductors and buntons. At the first stage, the profiles of the shaft and drawings of cross sections at various levels are prepared, and it is checked that the dimensions of buntons, points of connection of buntons, etc. correspond to the design specifications. Upon sinking the shaft, the profiling of the shaft walls (control survey) is carried out in order to determine the minimal gaps between the shaft lining and the most protruding portions of hoisting vessels. The

from Geological section ~DeptliMouth level +193.5 m Soil

Sections

surface, m

through

II

O

shaft

walls

III

IV

0

5

+30

10

+10

15

-10

20

+10

25

+20

0

Sand

30

+10

0

35

+10

-10

Floating earth

40

0

0

Clay shale

45

0

0

Sandstone

50

0

55

0

60

-10

65

-10

mm

Clay

~,

~ --

~ ~

Shale Coal

Fig. 9.31 Profiling of walls of vertical mine shaft: (a) arrangement of plumb bobs; (b) profiles of walls

~

;[;1 Sandstone

70 ,i~\;~(i~

-40

~

9.5.

Survey

Work

for Arranging

results of profiling are used for revealing the lining defects and making decisions on changing the scheme of equipment or eliminating the detected curvatures of the shaft. The profiling survey is done by measuring the distances from plumb bobs to shaft walls. The number and arrangement of plumb bobs are determined by the cross-sectional shape of the shaft and the arrangement of hoisting vessels in it (Fig. 9.31a). The measuring interval is usually taken equal to the pitch of equipment. The results of profiling are used for plotting the vertical profile of the shaft wall. The profile is drawn on a vertical scale (along the plumb bob line) of 1/100-1/200 and horizontal scale 1/10-1/20 (Fig. 9.31b). At the preparatory stage, the mine surveyor should also compile the scheme of arrangement and fastening of plumb bobs in the shaft, work out templates for the arrangement of buntons, and control the correct positioning of winches, pulleys, buckets and other mining and hoisting devices. At the second stage, the mine surveyor controls the design dimensions of the first bunton stage and then checks with especial care that the first bunton stage is mounted properly in its place, since plumb bobs will be later hung from it to control the positions of subsequent bunton stages. The correct mounting of the first bunton stage is controlled by measuring the distances from the shaft axes to the ends of each bunton, sleepers, and the points of connection of buntons and by levelling the ends of each bunton by a striding level. The displacement of the axes of buntons in the horizontal plane should not exceed 3 mm and the difference of the elevation marks of bunton ends, 5 mm. The number and arrangement of plumb bobs in a shaft depend on the scheme of equipment and arrangement of buntons. With the consecutive scheme of arrangement of equipment, plumb bobs are arranged against sleepers;with the combined scheme, they are arranged so as not to obstruct the placing

of Shaft

Equipment

223

Fig. 9.32 Schemes of plumb bobs for arrangement of shaft equipment

of conductors. The distances from the suspension points of plumb bobs tobuntons and side faces of conductors should not exceed 200 mm. A scheme of suspension of plumb bobs 1-6 for arranging the rigid equipment of a shaft of a unified cross section is shown in Fig. 9.32. The survey work for controlling the placing of buntons and suspension of conductors consists in checking the vertical distances between bunton stages, the positions of conductors and buntons relative to the horizontal axes of a shaft, the points of junction of buntons in a stage, and the positions of

~

224

Ch. 9. Surveying in Mine Construction 3~

p:C9

51

2F

D

lA 6

A-A

~

'r==' ~

88:z.tzA

Fig.9.33 Templates for arrangement of shaft equipment: I. 2. 3-spacing templates; 4. 5-vertical templates for marking holes for buntons; 6. 7- horizontal templates; 8- templates for correct placing of buntons relative to plumb bobs

plumb bobs proper. Since the positions of the characteristic points of the shaft equipment are repeated from one bunton stage to another, it is possible to employ templates for the control of mounting operations. The number and design of templates are chosen depending on the arrangement of buntons and plumb bobs and the technology of arrangement of the equipment. The templates are

usually made from steel sheets, angles or tubes. According to their application, templates can be divided into the following groups: (1) templates for marking the lengths of buntons and places of location of sleepers or mounting holes; (2) templates for placing the buntons at specified vertical distances from one another (spacing templates); (3) templates for

9.5.

Survey

Work

for Arranging

marking holes for buntons; (4) templates for coordinated arrangement of buntons in a stage (horizontal templates); and (5) templates for correct placing of buntons relative to plumb bobs. Some types of templates for these purposes are illustrated in Fig. 9.33. After mounting the equipment of a vertical shaft, the surveying of conductors is carried out in order to compile the profiles of conductors, buntons, and shaft walls. In this country, vertical shafts are surveyed by means of a complex for automatic control of the parameters of the equipment and lining. The complex comprises stations for the profile surveying of conductors, apparatus for the surveying of shaft walls, an instrument for measuring the safe spacings in mine shafts, apparatus for measuring the wear of conductors, and straightening instruments for the control of conductors. The stations are provided with instruments for measuring the angles of deviation of conductors from the vertical and distances between conductors and for checking the mutual arrangement of conductors in the shaft. Two instruments for measuring the vertical deviation angles are arranged at an angle of 90° to each other and mounted on carriages (Fig. 9.34) which are run along conductors. In this way, the angles of deviation of conductors in two mutually perpendicular planes are recorded. Records are made on 35-mm perforated photographic film together with the base line and elevations of buntons. The accuracy of measurements is 30" and the measuring range, :t20'. The instrument for measuring the distances between conductors is essentially a mechanical recorder fastened on one of the sections of the carriage. Records are made on a paraffin-impregnated tape on which one stylus draws the curve of deviations of the actual distances between conductors from the rated measure, whereas another stylus draws the base line. The elevations of buntons are also marked on the tape. The horizontal scale of 15~1270

of Shaft

Equipment

225

Fig. 9.34 Carriage: 1- box frame; 2 -detachable covers; 3- springs; 4- telescopic rod; 5- clamp; 6- s; 7- auxiliary safety rollers; 8- manual winding mechanism; 9-axles; 10-shackles

records of distances is 1I 1 and the vertical scale, 1/500; the measuring accuracy is :to.5 mm, the range of deviations of conductor spacings from the rated value is :t40 mm, and the range of measured distances, 350-3000 mm. The speed of motion of the carriage on conductors is up to 0.8 mls and the largest depth of shafts which can be profiled by this complex is 1700 m. The survey of conductors of a single compartment of a shaft 500-800 m deep requires only 0.5-1 hour. The photograms of deviation angles obtained in this way are processed in the office to construct the profiles of conductors. This is done by means of a semiautomatic integra-


Fig. 9.35 Integrator

Fig. 9.36

Aligning

inclinometer

9.5.

Survey

Work

for Arranging

",1

of Shaft

Equipment

227

partment, etc. The measuring range is from 0 to 500 mill and the accuracy of measurements is I5 mill. The apparatus illustrated in Fig. 9.38 is designed for continuous measurements of the wear of conductors and spacings between conductors. It contains two mechanical recorders which simultaneously the degree of wear of two conductors separately at each side of each of them and the spacings between the conductors. The apparatus can be used for measurements of conductors in combination with a station. In that case, the apparatus is connected to a carriage on which the instruments of the station are mounted.

Fig. 9.37 Profiling instrument: I-photographic camera cap; 2-measuring drum; 3-lock screw; 4- wide-angle objective; 5- handle; 6- illuminator

marked on 35-mm photographic film. The distance range of the instrument is from 0 to 3000 mm; the scale of recorded distances to the shaft walls is 1/25 or 1/50; and the root-mean square error of measured distances is I 5 mm in the range from 0 to 500 mm and I 10 mm in the range from 500 mm to 3000 mm. The instrument for measuring the gaps between the protruding portions of hoisting vessels and elements of shaft equipment is based on the same principle as the instrument for profile surveying, but has substantially smaller dimensions and mass. It is mounted on the top of a hoisting vessel or in a cage. The instrument can be set up for measuring the gaps between the guide paws of a hoisting vessel and equipment elements; the distances to the lining, tube stand, cables, ladder com15.

Fig. 9.38 Apparatus for continuous measurements of wear of conductors and spacings between conductors


When used individually, the apparatus is fastened to a hoisting vesselor to the hoisting cable of a mine hoist. The measuring accuracy is:!: 1 mm, the scale of recording 1/1, and the working speed of lifting or lowering in a shaft, 1-2 m/s. The survey work during mounting of a rope equipment consists in transferring the layout axes onto the mounting levels; checking the tensioning frame; control of arrangement of suspension clips, guide and tensioning devices;control measurements during mounting of auxiliary conductors; checking the track gauge of guides for hoisting vessels; and final surveying of shaft portions with hoisting and mining equipment. The layout axes of tower head-frames are transferred onto the mounting levels (headframe ceilings) by using the layout axes of a multi-rope hoisting machine. For jib-type head-frames, the axes are transferred onto the mounting level from the axial points by means of a theodolite and plumb bobs hung from a pulley stage. The axes of a shaft are transferred onto the fixation levels of guide ropes by means of plumb bobs at an earlier stage (during sinking a shaft). The discrepancies between the positions of axial marks obtained in two measurements should not exceed 20 mm on a suspension level and 50 mm on a fixation level. The arrangement of a tensioning frame and auxiliary conductors at loading levels is controlle.d relative to the layout axes of the fixation level of rope conductors and the axial points set up in the lining near the shaft bottom. The displacements of axes of buntons on a particular level should be not more than 3 mm in the horizontal plane, and the difference of elevations of the ends of buntons should not exceed 5 mm. The mounting of hoist clips and jacks on a suspension level is controlled relative to the axes of a shaft or multi-rope hoisting machine which are fixed on that level. The axes of these devices are laid out by the method of

ordinates. The design positions of hoist clips and jacks are denoted by axial marks op ing surfaces. Rope conductors are fixed in the vertical position by using a projection meter; for this purpose, the vertical sensor of the projection meter is fastened on a rope conductor above the tensioning frame. The final surveying of rope conductors is carried out after mounting the hoist clips and fastening the guide sleeves and consists in measuring the linear distances from the layout axes. The results of measurements are processed to compile a scheme of fastening of rope conductors on a head-frame ceiling and tensioning frame. The actual distances between the axes of ropes (devices) and layout axes should differ from the design values by not more than 7 mm. 9.6.

Survey Work During of Shaft Workings

Driving

The survey work during driving of underground workings near a shaft may involve certain difficulties, since such workings often have a rather intricate configuration with many ts, curvatures and with variable cross sections, combinations of straight and curvilinear sections, an intricate profile of haulage tracks, and contain large-sized stationary equipment units. Before constructing the shaft bottom, a design polygon on a scale of 1/200 or 1/500 is drawn (Fig. 9.39) which serves for checking whether the dimensions of underground workings are correct and for obtaining the initial data for the instrumental transfer of the axes of designed workings into nature. The drawing of such a polygon contains numerical data on the dimensions of straight and curved sections of workings, angles of turn of circular curves, elevations of particular pqints, etc. The axes of curved sections are replaced by chords whose number is chosen so that the

9.7.

Survey

Work

by Special

Methods

229

assigned from two side plumb bobs sunk into the shaft. The mining work for insetting a working is permitted at a distance not more than 40 m from a plumb bob sunk into the shaft. The working can then be driven further only after the points and bench marks of an ~ underground survey reference net have been fixed on its level. As the face is advanced in a working, the mine surveyor checks all parameters of the working being driven, marks the actual diFig. 9.39 Design polygon of shaft workings mensions of the working on a survey plate chords do not touch the lines of the walls of and compares them with the design dimensions, and determines the actual discrepanworkings. Check calculations determine the design cies. The discrepancies of the cross-sectional angles of a closed polygon and the coordinate area of a roughly driven working should be increases at all its vertexes. The check calcu- not more than 5-12% for a cross-sectional area up to 8 m2, 5-10% for an area up to lations are done by the formulae: 15 m2, and 3-7% for an area above 15 m2. ~13-180° (n -2) = 0, ~Ax = ~Ay = ° All cases of rock inrush and caving that where n is the number of vertexes of a took place during driving of a working are recorded in the mine surveyor's documents polygon. If the conditions described by these for- where their locations and main dimensions mulae are not fulfilled, the polygon should be are indicated. The voids left in the rock redesigned. Mter the plan adjustment of the massif due to inrushes and cavings should be polygon, a design profile is drawn, whose ed reliably and backfilled with noncharacteristic points are those where the combustible rocks in order to prevent further workings intersect one another or the angles rock displacement and the possible harmful of their inclination change. effects on the shaft lining. The insets of conjunctions of workings and Directions are assigned to workings by vertical shafts are determined after transfer- means of a theodolite and fixed by at least ring the elevation mark from the ground three plumb bobs hung at a distance not less surface onto the bench marks concreted in than 3-5 m from one another. Miners engaged the walls of the shaft. These bench marks are in the driving work can use the direction line usually set up somewhat above a conjunction defined by the plumb bobs on advancing to a so as to enable a convenient transfer of the distance not more than 40 m from the last elevation mark onto the roof (bottom) of an plumb bob. With a larger distance, instruadjacent working or onto the head of a track mental surveying is needed to set up new rail. Conjunction axes are usually transferred plumb bobs in the face. from two plumb bobs sunk from the surface, ' which define the axis of the shaft. This axis is 9.7. Survey Work During Driving fixed by means of two or three brackets of Vertical Shafts driven into the shaft walls somewhat above by Special Methods the level of the projected conjunction. The direction of inset for a conjunction Geological and hydrogeological conditions between the mine shaft and a working is of mineral deposits are not always quite


230

suitable for the construction of vertical shafts by conventional methods. In such cases, special methods are resorted to, in which measures are taken for strengthening the rock massif, ground water lowering, plugging and soil freezing, which can facilitate the driving of mine shafts. Under complicated conditions, vertical shafts can also be driven by drilling. In mine shafts driven by these special methods, the mine surv~yor has to solve certain specific survey problems. 9.7.1

Survey Work During Driving of Vertical Shafts with Artificial Rock Freezing

During driving of a mine shaft with artificial freezing of the rock, the mine surveyors perform the following operations: the layout of the centre of a shaft and the mouths of freezing and monitor holes; checking the construction of a drilling site, assembly and

position of drilling equipment, and the verticality of surface casings; surveying drill holes during drilling; and the compilation of level plans of ice-rock enclosure. The centre and axes of a shaft are transferred into nature by the method described in Sec. 9.2. The most popular method of layout of holes in the terrain consists in the following. A theodolite is set up at the centre of the shaft and oriented along one of the shaft axes, after which the required angle is laid off and distances to each drill hole are measured by a tape according to the design data. The accuracy of laying out of holes should be not worse than :J:50 mm. The mouth of each hole is marked by pegs. Before drilling the holes, a geometrical check is made (for verticality, centring above the hole mouth, linearity of the kelly, etc.) in accordance with the direction assigned by the mine surveyor, and the hole mouth is drilled for the surface casing. The length of the latter ,Jf

~

5'

Fig. 9.40

lnclinometric

level; 5- counterweight

station: 1- automobile block

3

with logging hoist; 2- inclinometer;

3- tripod; 4- striding

9.7.

Survey

Work

by Special

Methods

231

depends on the thickness of alluvium and upper caving rock and is usually of an order of 20 m. Before mounting a drilling rig, the rings of a drilling site are checked for horizontality by geometrical levelling at the top edge of the rings with an interval of 1 m. The. difference of height marks should not exceed 10 mm. A drilling rig is regarded to be ready for operation provided that the difference of elevations of the corner points of a platform does not exceed 5 mm; the error of centring of a rotary table above the hole mouth is not more than 10 mm; the difference between the height marks of the axial points of a rotary table is not more than 2 mm; and the deviation of the kelly in a rotary table from the vertical is not more than 0.001 of the kelly length. Deep vertical freezing and monitor holes can be surveyed by means of gyroscopic inclinometers which measure zenith angles in the range from 0° to 4-6° with an accuracy of 1.5-2' and direction angles, with an accuracy of 3-6°, The interval for measuring zenith and direction angles is not more than 30 m. Figure 9.40 shows an inclinometric station for measuring drill holes up to 1000 m in depth with a casing string and drill string of 96-127 mm in diameter. The station is mounted on a truck chassis, The main instrument of the station is an inclinometer (Fig. 9.41) with a gyroscopic direction stabilizer and zenith attachment for the orientation of the inclinometer from the surface. The measuring portion of the inclinometer consists of an azimuthal gyrostabilizer unit and zenith angle measuring unit. The latter has two penduli which make it possible to determine the zenith angle of the axis of a drill hole. The measured values of zenith angles are transmitted onto the surface. Fig. 9.41 stabilizer

Inclinometer

with gyroscopic

direction

~

232


The inclinometer consists of a housing 2, measuring portion 8, and guide rollers 1. The measuring portion includes the unit of azimuthal gyrostabilizer and unit for determining the zenith angle. The gyrostabilizer has a sensitive element 5, semiconductor amplifier 4, actuating motor with a reducer 3, and a m9tor with a rocker 7. When the inclinometer moves in a hole, there appears an external moment which rotates the housing 2 on the longitudinal axis of the instrument. This moment is transferred onto the measuring portion 8 and tends to turn the latter. Under this action, a gyromotor together with an angle sensor frame 6 deviates from the neutral position, and the sensor pulse is transmitted to the actuating motor 3. The motor develops (through the reducer) a compensating moment which retains the measuring portion of the instrument

~

Field sheet No.5 Shaft No.1

Hole No.3

JuneI5,'83900 M 110 01

g2S0r.1

HI

~ 1230 Or.2 02

"I 1

0;1

Fig.

9.42

Plate

with

inclinometer

in the given direction, so that its orientation is not changed. The unit for zenith angle measurements has two measuring elements which determine the zenith angles in two mutually poendicular planes. Each element has a flat pendulum 9 contained in a h()rmetically closed cylinder which is filled with a viscous liquid. Each pendulum carries the frame of an induction sensor; Surveying a drill hole is started from centring the inclinometer on a tripod above the hole mouth, after which the first orientation is carried out by means of an orientation attachment fastened on the inclinometer housing. For this purpose, a distinct object is chosen on the terrain at a distance not less than 30 m from the inclinometer, and the direction angle of this object relative to a line OlHl is measured (Fig. 9.42). The incli-

records

~

9.7.

Survey

Work

by Special

N

,

.--J e

5

26,

3

24/

~

23/ /

)~

,1

~ -;,~,

/'

,

3 \ \

(21( I ,201 --r19\

" ~, "

~

18

4 \ \

I--,

, 6'r

"

17

,

, 18'

\

'-14

the lines HlOl and 02H2. The angular correction is then introduced into the two orientation directions obtained during sinking and lifting of the inclinometer. The corrected directions are brought to coincidence in the points of the hole mouth, which gives two positions of the inclinogram. The results of surveying of freezing holes are used for plotting the level plans of an ice-rock enclosure (Fig. 9.43), which make it possible to estimate the thickness of the enclosure and determine the boundaries of frozen rock (to the centre and to the rock massif). The radii of ice-rock cylinders can be calculated by the formula: r = J(I/2

~ 16

~

..

,If ,f~ I

/

s Fig. 9.43 Level plan of ice-rock enclosure

nometer is then unclamped and sunk into the drill hole. As the instrument is being sunk, the planigraph records an inclinogram with elevation marks of depth intervals. Upon reaching the face of the drill hole, the orientation (inclination) of the inclinometer axis 0191 is recorded, and the gyrostabilizer is turned through 180° to record a new orientation of the inclinometer axis, 0292. Mter that, the inclinometer is lifted in the hole to make measurements from the bottom upwards. As the inclinometer appears on the surface, it is again oriented, and the direction angle of a line H2O2 is measured. The lines 0 1H 1 and H 20 2 are shifted parallel to themselves until points 0 1 and H 2 coincide. The angle 'Y formed by these lines (and called the angular correction) is determined graphically. A similar procedure is done for

233

Methods

+ af + k

where 1 is the spacing between freezing holes; a is the deviation of a hole from the vertical; k is a coefficient depending on the thickness of an ice-rock enclosure; it is taken equal to 0.6L for the inner boundary and 0.4L for the outer one (L is the thickness of the ice-rock enclosure as specified in the project). The permissible deviation of freezing holes from the vertical is 0.5 + 0.002 H, where H is the depth of a shaft, m; in all cases, the maximum deviation of freezing holes from the vertical to the shaft centre should not exceed 0.6 m. 9.7.2.

Survey Work During of Vertical Shafts

Drilling

The drilling method is used widely for driving of mine shafts. It allows one to mechanize completely the operations of rock disintegration and rock lifting onto the surface and eliminates the dangerous and hard work of underground miners. The method is mainly employed for shaft driving in soft water-bearing rocks (drift sand, water-bearing sands, chalk, clays, etc.); in coarse-grained sands, the method is not quite efficient in view of large losses of a clay drilling mud. Mine shafts are drilled by drilling rigs

234

Ch. 9. Surveying

in Mine

permitting the drilling out of the rock allover the face. Drilling a shaft is started from drilling a pilot hole of a depth exceeding by 5-10 m the design depth of the shaft and of a diameter of 0.5-1.2 m. The pilot hole serves for guiding the drilling tool in subsequent widening of the shaft. Upon drilling, the shaft lining is constructed by the float-on or sectional method. With the float-on method, a number of lining rings are mounted on one another on a reinforced concrete bottom plate. The cylinder thus formed is sunk into the fore shaft filled with washing fluid and floats, as it were, in the latter. New ring sections 4-6 m high are then put on top of the floating cylinder. After placing a ring section on the cylinder, ballast fluid is pumped in to ensure sinking the cylinder to a certain depth. After building the lining to the entire height of the shaft, the space between the lining and rock is plugged with a cement mortar. With the sectional method, a fixing section of the lining is first sunk onto a concrete pad prepared on the shaft bottom. Upon checking whether the section is placed correctly, it is fixed by a cement mortar poured into the space behind the lining. Mter that, the lining sections 15-20 m high are placed successively onto the fixing section and secured by pluggmg. Mine survey servicing during drilling of min shafts consists in checking the verticality of the shaft axis and observing that the lining is errected properly. The deviations of the shaft axis from the design (vertical) position should not exceed the spacing between the outer surface of the lining and the surface of the rock, which is taken equal to 200350 mm. The control of verticality of a shaft axis is complicated by the fact that the shaft is filled by clay drilling liquid during drilling. In shaft drilling without lifting the drilling tool onto the surface, the verticality is controlled by the position of the centre of the

Construction

drilling tool, which is done by the optical or geometrical method. With the optical method, the surveyor observes a light signal projected through a drill string; with the geometrical method, a cable is stretched through the drill string from the shaft mouth to the drilling tool, and its deviation is measured. In the former method, which is applicable at depths up to 200-250 m, use is made of instruments of the type of direction projectors. In the latter method, the deviations of the cable from the vertical can be measured at any desired depth with an accuracy to 20" by means of a projection meter. The error in the position of the cable relative to the drill string axis does not exceed 20 mm. Shaft walls are surveyed during drilling by means of ultrasonic locators which make it possible to take measurements in mud-filled shafts with an error up to 2% along the radius and 3%, in the orientation of a measured radius. 9.8.

Survey Work During Deepening of Vertical

Shafts

Deepening vertical shafts can be performed from the top downwards or vice versa. In the former case,the survey work is essentially the same as that during sinking of a shaft from the surface, though some specifics relate to the restoration and fixation of the centre and axes of the shaft in the deepened portion. Deepening a shaft from the top downwards can be done by one of three probable schemes: (I) under a platform constructed below the floor level of the working connected to the shaft bottom; (2) by means of a special ageway driven in the shaft portion to be deepened;and (3) through auxiliary workings driven sideways of the shaft. In deepening by the first scheme, the survey work consists in determining the centre and axes of the shaft in its section adjacent to the conjunction between the shaft

9.8.

Survey

Work

During

Deepening

/

0

l..v

I"

I:o'~

A-A -r--

b~ ~n

AL -=

11A

2l

t.k~~

W//////& Fig. 9.44 Restoration of centre and axes in deepenedportion of shaft through sinking agewayby meansof plumb bobs and theodolite and pit bottom, after which the restored axes are fixed by brackets below the future platform. In that case, the centre of the shaft is determined by the point of intersection of wires stretched between the brackets that fix the shaft axes. With the second scheme of shaft deepening (Fig. 9.44), the survey work is started from determining the centre and axes of the shaft in the bottom portion, by using the points of an underground survey reference net. The centre and axes are transferred under a pillar by means of plumb bobs 01 and O2

of Vertical

Shafts

235

(see Fig. 9.44) whose coordinates are determined from the points of the reference net of the workings near the shaft bottom. Mter cutting a chamber under the pillar, the centre and axes of the shaft are laid out by means of plumb bobs 01 and O2. For this pu~ose, the theodolite is set up in a point A which is chosen so that the shape of a connection triangle A01O2 can be convenient for solving the junction problem. The theodolite is sighted at points 01 and O2, and points a and b are marked on the shaft walls. Solving the connection triangle A01O2, it is then possible to determine the coordinates of the point A and the direction angles of lines A01 (Aa) and A02 (Ab). The coordinates of the shaft centre determined at the level of shaft workings and the coordinates of the point A just found are used for solving the inverse geodetic problem of determining the layout angle aAC and the distance AC. By constructing the angle aAC and distance AC in nature, we then determine the position of a point C, the centre of the shaft, which is then transferred and fixed in the safety pillar. With the known direction angles of the shaft axis and of direction CA, we can now calculate an angle ~ and lay it off from the direction CA by means of a theodolite set up in the shaft centre point. The direction of the shaft axis determined in this way is fixed by brackets on the shaft walls. The transfer of the centre and axes of the shaft under the safety pillar is performed twice. The discrepancies between the two results should be not more than 5' in axial directions and not more than 20 mm for the position of the shaft centre. If a shaft is to be deepened through auxiliary workings driven beyond its limits (winzes, blind pits, inclined workings, etc.), the coordinates of the shaft centre and the direction angle of one of the shaft axes are determined on the desired level from the points of an underground reference net (H and D in Fig. 9.45). A polygonometric

236


A-A

p Fig. 9.45 Transferring centre and axes in deepened portion of shaft through winze

traverse is then run from these points to the auxiliary working. In the case illustrated in Fig. 9.45, the auxiliary working is oriented by means of plumb bobs 01 and O2. This orientation makes it possible to find the direction angle of a certain direction fixed by points A and B on the level to which deepening should be done. The coordinates x, y of these points are also determined. With the known coordinates of the shaft centre and the coordinates of the point B of the polygonometric traverse on the lower

level, it is possible to solve an inverse geodetic problem and calculate the layout angle ARC = 13and layout length RC = I, which are laid off in nature and determine the position of the shaft centre. Then, as in the previous case,the direction of one of the shaft axes is assigned and fixed by points F and G. For a shaft to be deepened from the bottom upwards, the coordinates of the shaft centre and the direction angle of the shaft axis are determined before starting the layout work. The survey work in the workings on

9.8.

Survey

Work

During

Deepening

the level of deepening is also carried out. All measurements essential for laying out the centre and axes of the shaft on the level of deepening are carried out. The centre of a shaft on the lower level is usually fixed in the foot of a working, and the shaft axes are fiXed by brackets in the walls or roof of the working. The verticality and cross-sectional area of the shaft are checked by means of plumb bobs hung under the sinking platform from brackets in the temporary lining. The

of Vertical

Shafts

237

positions of the plumb bobs are checked by measuring the distance between them and the centre of the shaft. The centre of the shaft in the face is found by means of templates or measurements from temporary plumb bobs which are centred above the permanent plumb bobs. The shaft should be checked for verticality in every 3 m of face advance, and the shaft axes should be transferred onto the brackets of permanent plumb bobs after every 10 m of shaft advancement.

Chapter

Surveying

10.1.

General

The principal aims of the mine-surveying service in open-cast mining are as follows: the provision of the geometric basis for the surveying work in the form of a reference net; surveying of mining workings and land surface; compilation of graphical documents for the normal operation of a mining enterprise; participation in the planning of drilling and blasting; control of the specified parameters of working systems and the dimensions of structures; calculation of the output of a mineral, volume of burden rock, dynamics of losses and the dilution of a mineral; observations on the motions of quarry flanks and development of measures for their prevention. The results of mine surveying are used for compiling calendar plans of mining work development, investigations of the geological structure of deposits, solution of various problems associated with the activity of production sections, etc. The objects of surveying in quarries include the following main groups: (a) exploratory, draining and drillingblasting workings, crests, accesstracks, working trenches, catchwater ditches, etc.; (b) tectonic disturbances, s of the lying and hanging wall with the mineral, boundaries of sections with different grades of ore or different ash content of coal, assaying points, boundaries of landslides, etc.; (c) haulage lines in a quarry, pay-ore area

Ten

in Quarries

structures, hoists, trestles, power transmission lines, pulp pipelines, etc.; (d) flooded workings, cavities left after underground mining work, fire zones, etc. 10.2.

Reference and

10.2.1

and

Surveying

Mine-Surveying Nets

Survey

Nets

Work

Reference

Mine-surveying reference nets on deposits extracted by open-cast methods are developed in accordance with the requirements set forth to reference nets on the land surface for the territories of economic interest of mining enterprises. They may include triangulation points, trilateration points, and polygonometric points. Levelling bench marks can be used as the reference basis for surveying nets in quarries. Modem organization of mine surveying in open-cast mining of deposits is characterized by that the work proceeds successively 'from the general to particular', with measurements at each stage of the work being made with the specified accuracy. On the land surface of a mining enterprise, a reference net beyond the limit of the design contour of a quarry is formed initially. After that, as the mining work is developed on the quarry flanks, and sometimes inside a quarry, reference points are set up in these places, which are called approach points and serve for the formation of a surveying net.

~

10.2.

Reference

and Survey

Nets and Surveying

239

Work

,"

A

,I

2

3 '>f'

/-~

~2'

"1' ~.J 6

\

B

Fig. 10.3 Construction of reference net by poly. gonometry --

~ c

Fig. 10.1 Insertion of point into development of reference net

rigid

angle for

Depending on the configuration of a quarry, local conditiQns, methods of stripping and provision of technical facilities, the approach points can be determined by the methods of triangulation or polygonometry. The method of triangulation is employed in cases when approach points are readily visible from reference points. In such cases,use is most often made of the insertion of one (Fig. 10.1)or several points into a rigid angle, construction of a chain pf triangles between two fixed points (Fig. 10.2) or the construction of a geodetic quadrangle. In triangle chains, the number of figures should be not more than five. The angles of triangles should JA

'/134

6

.~B

-, ,

1 /"7

)

~

\

I

13\

2 """

fi5y I 1'10

M

R 1"12

~L~

N

4

3 Fig. 10.2 Construction of chain of triangles between two reference points

be not less than 30° in chains or 20° in geodetic quadrangles. The method of polygonometry is resorted to in cases when there is no visibility between the reference points and the points to be determined (approach points), but the land surface is quite convenient for linear measurements to determine the approach points. The polygonometry can also be used with successon a rough terrain if it is possible to employ light or radio range finders. Polygonometric traverses are commonly run between the points of a mine-surveying reference net (for instance, points A, B, and C in Fig. 10.3). 10.2.2.

Surveying

Nets

Surveying nets are constructed on the basis of points of a reference net. In surveying the land surface, waste dumps and quarries, surveying nets are constructed according to the following requirements: the main points of a surveying net should cover evenly the survey surface area; their density is determined so as to have four points per km2 in surveyings on a scale 1/5000, 10 points per km2 on a scale 1/2000, or 16 points per km2 on a scale 1/1000; each surveying plate made on a scale 1/5000 should have at least three main points fixed by permanent centres; two such points are sufficient on plates on a scale

240

Ch. 10. Surveying in Quarries

of 1/2000 and one such point, on those on a scale 1/1000. Depending on the terrain relief, shape of a quarry in plan, mining technology and some other factors, surveying nets can be constructed by the following methods: method of geodetic intersections; method of analytical nets; method of theodolite traverses; method of range lines; polar method; and method of a rectangular network. Since a survey control net has to exist only for a relatively short time, it can be fixed by permanent or temporary points in the form of wooden page or metal rods driven into the soil. In hard rocks, temporary points are usually fixed by cross marks made on the protruding portions of the rock. Survey points are usually located on the lower platform of each working bench at distances not more than 400 m from one another. Method of geodetic intersections is em-' ployed in cases when the points of a surveying net are located at appreciable distances from those of a reference net. Right and side intersections and reverse intersections (resections) are usually employed. Right and side intersections are drawn from at least three initial points. A resection is drawn from four points, provided that the point to be determined lies near the circle ing through three of the four initial points. The coordinates of the points determined by r.ight or side intersections are calculated from two triangles; in the method of resections, they are found from two versions. In all cases,the final coordinates are taken as the arithmetic means from two measurements. The maximum discrepancy should not exceed 0.8 m. Method of analytical nets is employed in quarries where both flanks are working (moving). Analytical nets are constructed as chains of triangles or other figures (geodetic quadrangles, a central system, etc.) which are ed by sides and points of a reference

net. Triangle chains and central figures are used most often. The latter are employed for constructing a surveying net on the lower levels of quarries of a small area or of some portions of a quarry, whereas triangle chains are preferred in the quarries of an elongated shape and appreciable depth. The number of points detennined by an individual triangle chain or figure should be not more than seven. Triangles should have a shape close to equilateral. The angles at the points being determined should be not larger than 120° or smaller than 30° and the side lengths, not smaller than 300 m or greater than 1000 m. Angular measurements are commonly made by means of theodolites. The permissible angular discrepancy in triangles with the side length up to 1000 m is l' and in those with the side length more than 1000 m, 40". Method of theodolite traverses is employed in quarries having a large extention of the front of mining and stripping work and benches of a form convenient for linear measurements. Theodolite traverses are run between two known points A and B (points of a reference net) or between closed polygons. At junctions of theodolite traverses to the initial points, there are measured the angles between the junction side of a theodolite traverse and two directions onto the points of a reference net (Fig. 10.4). The distances between the points of theodolite trayerses should not exceed 400 m and, as a rule, should be less than loo m. The length of a traverse should be not more than 2.5 km. The angles in theodolite traverses are measured by theodolites. An angular discrepancy should not exceed f fJ= 30"J~ , where n is the number of measured angles. The three-stand scheme can be recommended for angular measurements. The theodolites should be centred with an accuracy not worse than 2-3 mm. The length measurements in theodolite

10.2.

Reference

and

Survey

Nets

and

Surveying

Work

241

Fig. 10.4 Providing survey control by means of theodolite traverses

traverses can be made by means of steel or cloth tapes or range finders. In some cases, the lengths of traverse sides can be determined by indirect methods, but in all casesall measurements should be done in the forward and reverse direction, and the relative difference between two independent measurements should be not more than 1/1000. The linear discrepancies in theodolite traverses should be not more than 1/3000 of the traverse length. The corrections for temperature, tape standardization, and horizontalization of lines should be introduced into the measured lengths. A temperature correction is introduced in cases when the temperature at measurements differs by more than 5 deg. C from that at which the tapes have been standardized. A correction for horizontalization is introduced when the inclination angle is larger than 10. Linear measurements can also be carried out by the optical method with the use of optical range finders and range finder attachments and a base-measuring (subtense) bar. In some cases when the form of benches is inconvenient for length measurements on the ground and optical range finders are not 16-1270

available, it is possible to measure the lines of a theodolite traverse by the indirect method of geodetic intersections which is essentially as follows. A theodolite traverse is run on the working platform of a bench and connected at the ends to the points of a reference net (I, II, Fig. 10.5).Auxiliary points A, B, and C are chosen at certain distances away from the theodolite traverse line. Angles ~1' ~2' ~3' ..., ~17 are measured from the points of the theodolite traverse line and lines I-I and 6-1I, which are the refere~ bases, are measured by a tape. The side l-A of a triangle IAl is calculated by the sine theorem:

A-l

1-2=

sin P4

sma2

In a similar way, the side 2-3 is calculated, which is the connecting side for solving the triangles constructed from the point B. The calculations of the next series of triangles give

242

Ch. 10. Surveying

in Quarries

~ I B

C

A

I'~ \

/~,

\\

~,

l~n

~ (15

i

6

\

"

a-,'l:

! ):

I

~17 ~

8m

\

\

{,

I ,

I Pel

"

Fig. 10.5

Indirect

measuring

of sides of theodolite

a side 4-5 which is the basis for solving the last series of triangles constructed from the point C. A check is done in this method by comparing the calculated length of the last line of a theodolite traverse, 6-11, with its length measured in the field. Method of range lines is employed in quarries where the working front is advanced in one direction only, so that the reference points fixed on the non-mining flank can be easily observed from the working benches. This method is especially convenient in cases when the platforms of working benches have a certain elevation above the ground surface of the opposite flank of a quarry (Fig. 10.6). For laying out a range line, a secondorder .polygonometric traverse is first run (A, B, C, ..., G). With the known direction angles of range lines, it is possible to calculate the angles 'I' and

traverse

nates of the point p 1 are found, In order to have an optimal shape of triangles, it is essential that the angles a and 13 be not smaller than 30°, If however these angles are smaller than 30°, it is possible to sight the instrument at reference points located on adjacent range lines (for instance, a point p 2 and sighting at points B and F). Polar method of providing survey control has become popular with the appearance of 123 y III I A ~~~

456 ~ I B

~ 111 I C

~ IV I D

7 I v

~ VI I F

~ VII I G

~

-7 Oj:l=.:

JJI.::.--I~

-:::.

1--

~ P2

Fig. 10.6 Providing range lines

survey control

;:J by method of

~

10.2.

Reference

and

Survey

Nets

and

Surveying

A<

243

Work

,

(

e

I

oB

[3

4

Aa< \{5 l5 \

.2 I

b\

I

~

~

~

2

DO

~

.

j Fig. 10.8 Providing rectangular network

geodetic light range finders. For successful application of this method, a greater portion of a quarry must be readily visible from a few number of points ofa reference net. For the construction of a surveying net, a light range finder i.s set up on a point (A) of the reference net, and light reflectors are set (Fig. 10.7) up on surveying net points 1, 2, 3, ...which are to be determined. Upon measuring the distances, the light range finder is replaced by a theodolite to measure polar angles ~l' ~2' ~3' etc. Method of a rectangular network for the construction of surveying nets is applicable in quarries of a shallow depth and with a flat relief of the surrounding land. A network of rectangles is laid out on the territory of deposit, and survey points are fixed in their corners (Fig. 10.8).It is a common practice to layout two systems of rectangles: the main network with the side length d equal to 50 m, loo m or 200 m and the densifying network of rectangles with the side length dl equal to 5-40 m, which is used directly for surveying. The orientation of the sides of a network is

survey control

~c by method

of

chosen parallel (perpendicular) to the main mining front or coincident with the orientation of a coordinate network. For laying out a rectangular network, a plan of the surface is compiled, which gives the technical boundary of a quarry and a number of reference net points (1, 2,3,4, 5) near it. Then the directions of the axes of a rectangular survey net are chosen, the rectangular network is laid out, and the coordinates of its corners are calculated on the plan. After that, a project of the densification of the reference net is designed so that its points can be as close as possible to the corners of the rectangular network; the densification network is transferred into nature and fixed on the ground. The corners of the network can be fixed by laying off the distance and direction angle from the closest reference point or by the method of angular intersections with the use of one or two theodolites (see Fig. 10.8). For the transfer of surveying net points onto the lower levels of a quarry or the restoration of annihilated points, use is most

244

Ch. 10. Surveying (a)

in Quarries

(b)

L--L. r--r-

:J=' --r-! .+-~ , ~

'

.(, ~-+ L Fig. 10.9 Transfer angular intersection

(restoration)

of surveying

net points: (a) by method

often made of the method of range lines in which two theodolites are set up on two closest existing points (Fig. 10.9a),and a new point is fixed at the intersection of their collimation lines. It is also possible to use the method of direct angular intersection. In that case the position of a point of the reference net is determined on the ground by laying off two horizontal angles ~1 and ~2 by means of two theodolites (Fig. 10.9b); the sought-for point is then found at the intersection of the collimation lines of the two instruments. 10.2.3.

Elevation

Control

of Quarries

Elevation control is required for determining the heights of the points in a quarry. The heights of the points of a surveying net are measured by geometric or trigonometric technical levelling. Geometric levelling is usually employed in quarries with railway transport. Technical levels and levelling staffs of any type are suitable for the purpose. Technical levelling between the points of a reference net may be done in one direction only; hanging lines are permitted, provided that they are run in the forward and reverse direction. The readings in levelling are taken only relative to a single line. The difference of elevations determined on the black and red face of staffs should not exceed 10 mm. The permissible discrepancy of level lines is

1

, --1 !

of range lines; (b) by method

of

50JL mm, where Lis the length of the level line, km. Trigonometric levelling has found use in quarries with railless transport and in cases when a surveying net is formed by the method of geodetic intersections. When det.ermining the elevations of points by trigonometric levelling, vertical angles are measured by means of theodolites at the same time with measuring the horizontal angles; the accuracy of reading-off devices of the vertical circle of the instruments should be not worse than 30". The heights of an instrument and sighting target should be measured with an accuracy to 1 cm. The measurements of vertical angles can be controlled by the constant place of the zero point of the vertical circle. The deviations of the zero point should be not greater than thrice the reading-off error on the vertical circle. Trigonometric levelling lines should be connected to the points whose elevations have been determined by geometric levelling. Their length should not exceed 2.5 km. The permissible discrepancy between a forward and reverse elevation is not more than 0.041cm where I is the length of a line, m. The discrepancy of a levelling line, cm, should be not more than mh = 0.04[1]/J~ where [I] is the length of the levelling line, m, and n is the number of levelling lines.

10.2.

Reference

and

Survey

If the points of a surveying net are determined by the polar method or method of geodetic intersections, the elevations between the points are found by trigonometric levelling in the forward and back direction or in a single direction only, but from at least two points. In such cases,elevation discrepancies (in centimetres) should be not more than 0.031for distances up to 1 km or 0.021for distances above 1 km (where 1 is the length of the lines, m). If a side in one-sided levelling exceeds 700 m, a correction for the Earth curvature and refraction should be introduced into the measured elevation. 10.2.4.

Surveying

in Quarries

The surveys of quarries and complementary surveys of benches can be carried out by the following methods: tacheometry, method of perpendiculars, plane-table survey, stereophotogrammetry, and their combinations. For the compilation and complementation of mining working plans, it is advisable, where possible, to perform aerial and ground stereophotogrammetric surveys. Tacheometric survey is employed for: (a) surveying of quarries where the mining technology is such that the volume of extracted burden rock and that of the mineral in the pillar can be determined directly from the results of bench surveying; (b) for surveying of quarries of a relatively low capacity; (c) for surveying of'dead' spaces obtained in ground stereophotogrammetry; and (d) for check surveying of mining workings in the selective control of their plan positions and for surveys in cases where stereophotogrammetric methods are inefficient or inapplicable. Plane-table survey has found no wide application. It is mainly used for single surveys of small quarries or their portions when a general plan of mining workings is to be compiled.

Nets

and

Surveying

Work

245

The periodicity and sequence of surveys in quarries are as follows: surveys of contours of bench crests and blast holes are made only in places where blasting work is to be performed. All other objects except for mineral stores are surveyed only when a need arises. Mineral stores are surveyed every ten days or once a month depending on the method adopted for calculating the amount of the extracted mineral. Surveys in quarries are made from the points of a survey net. The distances between these points on a bench should not exceed 300 m for a scale 1/1000 or 400 m for a scale 1/2000. It is permissible when needed to determine the additional points of a surveying net by running a single-sided hanging theodolite traverse. The length of sides should be not more than 300 m in surveys on a scale 1/1000 or 400 m on a scale 1/2000. The staff is set up on all characteristic points of the contours and surfaces being surveyed. In surveys on a scale 1/1000, the distances between the staff points should not exceed 20 m for the bench crests of intricate shape or 30 m for the extended crests. In surveys on a scale 1/2000 the respective distances are 30 m and 40 m. In the surveys of the surface of blasted rock the distances between the staff points should not exceed 10 m for a scale 1/1000 or 20 m, for a scale 1/2000. A sketch of bench contours is drawn at each survey station (Fig. 10.10a). A sma[[-sized geo[ogica[ a[timeter (Fig. 10.11) has been developed in this country for the geological documentation of quarry benches. The instrument is intended for the remote measurements of vertical thickness and dip angles of visible seams. It can also determine the relative elevations of the position of geological elements and other objects. The altimeter is essentially an opticomechanical goniometer provided with a direct-image telescope and self-adjusting verti-

246

Ch. 10. Surveying

(a)

in Quarries (b)

~ ~~-,I.:Lg--~

-13

o-~~

: 10--:~--

:~

("I

"' ("I.

i ("II

~ ~ c.; c-.

LO (I)

v.:.-~

39.71-

-~

;15

0: ~

-:.~,;~5~~

~

3

\

~I--

--'0

ir::::njt1r~ Fig.

10.10

Sketch of bench contours:

(a) by tacheometric

cal circle with scales of elevations and vertical angles. The working portions of measuring scales are visible directly in the telescope. The range of measured elevations is :t 10 m for a sighting length up to 10 m or :t 20 m for a sighting length of 20-40 m. The range of measured visible dip angles is :t 90°. The error in the measurements of the vertical thickness of seamsis not more than 5 cm and that of the visible dip angles of seams, 1°. The mass of the instrument is 1.5 kg. Method of perpendiculars can be employed efficiently for the surveys of bench crests with simple contours when the required number of staff points is not large (Fig. 10.10b). The surveying net for the method of perpendiculars is constructed in the form of theodolite traverses or as a rectangular network. The length of ordinates, as a rule, should not exceed 30 m. For a length more than 15 m, they should be set up by means of a right-angle mirror. Lengths are measured by tapes and rounded off to decimetres. The distances between the staff points are chosen according to the recommendations given for tacheometric surveys. Stereophotogrammetric surveying of quarries. In recent time, stereophotogrammetry has come into use in many quarries in place of tacheometric surveying, which offers the following advantages: (a) increases the labour productivity of the field work;

method;

(b) by method

of perpendiculars

(b) eliminates the need in staffmen and thus increases the safety of work; (c) provides a large choice of points in compiling plans by photographs and thus better characterizes the section surveyed; and (d) involves all visible objects including those which are inaccessible for tacheometry.

Fig. 10.11 Geological altimeter: l-eye-piece; 2-housing; 3-adjusting level; 4-reading-otT magnifying glass; 5- horizontal circle; 6- base; 7-levelling wedges;8-handle; 9-horizontal sighting screw; 10-vertical sighting screw; ll-telescope; 12-focussing device

10.2.

Reference

and

Survey

Ground and aerial stereophotogrammetry can be employed. Ground stereophotogrammetry can be used either independently or in combination with tacheometric surveying. Stereophotogrammetry can determine and represent graphically the shape, dimensions, and spatial positions of objects and relief of the Earth's surface. It is especially efficient in large quarries. To compile a plan of a quarry section, this section is photographed stereoscopically from two points at the ends of a base S1S2 (Fig. 10.12). The two photographs of the same portion of land, when viewed through a stereoscopic device, produce a three-dimensional effect. When made from two ends of a base line they represent a stereoscopic pair whose principal elements are as follows: (1) the left-pand (PJ and right-hand photograph (P 2); t2) the centres of projection of the left-hand and right-hand photograph, SI and S2' or the rear optical centres of the two objectives of stereophotogrammetric camera; (3) the photographic base Bph = S1S2 which is also equal to the distance between the centres of projection of the photographs; (4) beam bundles alSlA, ~ISIC, a2S2A, C2S2C,etc., i. e. the combination of projecting beams which form images on the photographs; (5) the main beams S101 and S202 which are perpendicular to the planes of photographs; (6) the main points 01 and O2, i. e. the points of intersection of the main beams with the planes of photographs; (7) identical points a1 and a2' c1 and C2' etc.; (8) the images of the same point on the land on the photographs of a stereoscopic paIr; (9) corresponding beams Slal' S2a2' etc.; and

Nets

and

Surveying

247

Work

A

c

I 'I

s -1J / 'y-

f!i!f: 1

/

~

10.12

~S ,11\ 2

~

a C1

Fig.

~

B~h

J I

Elements

of stereoscopic

a., C2

pair

(10) the focal distances of photographs !1 = 8101 and!2 = 8202. In stereophotogrammetry, the'position of a point on the land is determined by a direct spatial intersection which is formed by the projecting beams ing through tq~ leftand right-hand point of the base. For instance, the position of a point C (see Fig. 10.12)can be determined if the directions of projecting beams c181C and c282C are known. The surface formed by the plurality of the points of intersection of corresponding projecting beams is called the geometrical model, or simply model. Photographic cameras for making stereophotographs are provided with devices which ensure their definite and fixed position during exposure. A photographic camera can also be combined with a theodolite, and the combination is called a photo theodolite. The stereophotogrammetry of quarries can be performed from a fixed base on the

248

Ch. 10. Surveying

ground or from a flying object (aeroplane). It is distinguished between two principal cases of ground photogrammetry: with a horizontal position of the optical axis of a photographic camera (horizontal stereophotogrammetry) and with the optical axis inclined substantially relative to the horizontal (oblique, or perspective, stereophotogrammetry). Horizontal stereophotogrammetry is easier to make and has an essential advantage over the oblique method, since the latter requires more intricate techniques of photoreading. Horizontal stereophotogrammetry is usually done as a combination of three cases: with the optical axis of a photographic camera directed perpendicular to the base and deviated by 30-35° to the left and right from this position (Fig. 10.13). The coordinates of points on photographs are determined in a rectangular system of coordinates (x'x' and z'z' in Fig. 10.14).The point of intersection of coordinate axes, 0', is the origin of coordinates. The coordinates of a parti<;ular point a, as measured on a photograph, are commonly called the photocoordinates (xa, Za). Coordinate marks are fixed so that the point 0' which is the origin of coordinates, and the main point 0 of a photograph, are perfectly coincident. In that case, the coor-

Fig. 10.13 Horizontal survey

stereopho togrammetri c

in auarries

dinates of the main point, Xo and Zo, are equal to zero. The coordinates of points on the land are determined in the coordinate system adopted for a quarry. In contradistinction to photocoordinates, they are designated by capital letters xYZ. The coordinates of points on the land are determined on photographs according to the positions of the bundles of projecting beams at the instant of exposure. The characteristics that determine the positions of beam bundles are called the elements of the orientation of a photograph (which are subdivided into external and internal). The elements of internal orientation include the focal distance (focal length) of a camera and the coordinates of the main point Xo, Zo. Among the elements of external orientation (Fig. 10.15)are the coordinates of the left-hand end of a photographic base, Xs , ys and Zs ; the angle of inclination of thelmaih beam 6f the left-hand photograph, (J)1;the angle of turn of the left-hand photograph in its plane, "1; the oblique angle of the left-hand photograph
Fig. 10.14 Coordinate system of photograph

10.2.

Reference

and

Survey

Nets

and

Surveying

249

Work xph

Yph

/

ZPh

//

/ /~

:..'

/ //

/

1112

(111

~

/

HoLta,

/

x ~

x

,.../

01 ys

z

190 8 ~ ,

S1 i

xI I X

,.ls, I

---1

/

,I

B

./ Xph

I':/ / / Xs1

/ ff 2

Base

,

~

c --\-"'

/

z x

/

/

2 /

02

/

Horizontal.11

X

X2

1

Fig. 10.15 Element of external orientation of stereoscopic pair

base QB; the projection of the photographic base onto a horizontal plane; the height difference of the right-hand- end of the photographic base above the left-hand end, Az; the angle 'of inclination of the main beam on the right-hand photograph, m2; the angle of the turn of the right-hand photograph in its plane, "2; and the angle made by the main beam projections of the photographs onto a horizontal plane, y (Figc 10.16). With a positive angle y, the main beams are convergent, and the angle y formed by them is caned the angle of convergence; with a negative y, the main beams are divergent, and y is called the angle of divergence. The coordinates Xs , ys , and Zs , the photographic base Bp~, arid its dirbction angle QBare determined by geodetic methods. The oblique angles of photographs are set up by the orientation device of a phototheodolite. The inclinatio~ angles of the main beams of photographs, m, and the angles of the turn of photographs, ", are reduced to

nearly zero values by means of spirit levels mounted on the camera. The mine-surveying plans of land surface and mining workings art: usually constructed in a left-hand system of coordinates, whereas stereophotogrammetry employs a right-hand coordinate system. In both cases, however, the z-axis is arranged vertically. Let us analyse a case of normal stereophotogrammetric survey (see Fig. 10.16) in which the optical axes of the photographic cameras set up in points SI and S2 are parallel to each other and perpendicular to the photographic base Bph. It is assumed in this example that: (a) axis Xphcoincides with the direction of the photographic base; (b).axis yph coincides with the direction of the optical axis of the photographic camera set up in the point SI (the left-hand end point of the base); and (c) axis Zphhas a direction perpendicular to the plane formed by the two other axes.

250

Ch. 10. Surveying

in Quarries

-:4

<

"-

~

Fig. 10.16 Normal stereophotogrammetric survey

We have to determine the photogrammetric coordinates of a point K on the land. Let the image of the point K on the left-hand photograph be denoted by k, and that on the right-hand one, kr (see Figs. 10.16 and 10.17). The designations adopted in the figures are as follows: Yph'Xph'and Zphare the photogrammetric coordinates of the point K on the land (Yphis also called the distance to the point K); XI is the abscissa of the point k, on the left-hand photograph; Xr is the abscissa of the point kr on the right-hand photograph; ZI is the ordinate of the point k, on the left-hand photograph; Bph is the photograI'hic base; and fc is the focal length of the photographic camera of a phototheodolite. Noting the similarity of triangles KK'Sl and k,k~Sl (see Fig. 10.17), we can write: Yphlfc= Bphl(XI -Xr) Denoting X, -Xr = p (which is called the horizontal parallax, or x-parallax), we can write the formula in the form: BpJc Yph=-=-

xi -Xr

Bp,jc

p

(10.1)

..A'

From the similarity of triangles SlOK and Slojkj, it may be written: Xph/Yph= Xj/!c

or

Xph= (Xj/!c)Yph

Substituting for Yph' we get: Xph= BphX,/P

(10;2)

Similarly: Zph= BphZj/P

(10.3)

As follows from these formulae, in order to determine the photogrammetric coordinates Yph' Xph' Zphof points, one has to know the photographic base in nature and the focal length of the photographic camera of a phototheodolite and to find on the photographs the values of X" Z" and p. The length of a photographic base, the distance from the photo theodolite to the objects being photographed, and the focal length of a photographic camera are considered the principal parameters of a stereophotogrammetric survey. All objects of a stereophotogrammetric survey should always lie within a range between the minimum permissible distance Yph .and the maximum permissible distance mln

10.2.

Fig. 10.17 Y ph

Determining

from

the

Reference

and Survey

photogrammetric

pho-tographic

base.

coordinates The

for-

max mer IS needed "lor the appearance of a stereoscopic effect and the latter ensures the specified accuracy of measurements. The minimum permissible distance depends on the technical characteristics of stereoscopic devices and the specifics of the stereoscopic vision of an observer. It can be determined by the formula:

Yph

.= mln

(3-4)Bph

(10.4)

The maximum permissible distance is found by the formula: Mfc ~ Yph

= max

1.25-tmin loo

Nets and Surveying

(10.5)

where fc is the focal length of a phototheodolite; M is the denominator of the scale of the plan to be compiled; tmin = COS~ = = (x2/fc)sin~ (here ~ is the oblique angle of a photograph and X2 is t~e largest coordinate x on the right-hand photograph within the limits of the stereoscopic pair working stage).

of point

Work

251

on terrain

Depending on the length of the photographic base, accuracy requirements, and possibilities of photoreading, the length of the photographic base can be determined by one of the following methods: (I) if a quarry or land portion is surveyed for mapping, the base can be calculated by the formula: 2 B=Q~ (10.6) Mfctmin where y f is the distance to the farther boundary of the working portion of a given stereoscopic pair and Q is a coefficient which is taken equal to 15 for a single survey of a quarry and to 20 for mapping of the land surface; (2) in monthly complementary surveys for calculating the volumes of excavator cuts, the base length is found by the formula: y} . Bph

=

1.8 Mfcdmvtmin

( 10.7)

252

Fig.

Ch. 10. Surveying

10.18

Determining

useful

area of stereogram

where d is the width of a cut, m; mv is the specified root-mean square error of the volume measurement, %; and YI'fc, tmin and M as in formulae (10.5) and (10.6). It is also essential to know the overlapping area in a stereoscopic pair taken from a particular photographic base. Consider, for example, the photographic base SlS2 (Fig. 10.18). We construct the horizontal vision angles (working angles) a of a phototheodolite on the land from the ends of the base. The useful area F us' confined by points abcd, is depicted on each photograph of the stereo pair and later processed in a stereocomparator. It can be written by reference to Fig. 10.17: Fus= (D/t)(Lmin + Lmax) (10.8) where D is the depth of a survey; Lmin is the closer base of a trapezium; and Lmax is the farther base of a trapezium. The trapezium bases can be found by the formulae:

(

a Bph Lmin = 2tan 2 3.5Bph-Tcotan

Lmax = 2tan-

a 2

(Yph max

Bph --cotan2

a

2 a

) )

(10.9)

(10.10)

2

Noting these expressions, the formula for the useful survey area will be as follows:

in Quarries

(10.11) Ground stereophotogrammetric surveying includes reconnaissance, geodetic measurements, and land photography. Reconnaissance is done for selecting the locations of the points of a referenee net, photographic bases, and fiducial (correcting) points. Since the length, number and dire:c!tion of photographic bases can influence substantially the productivity of the survey work, it is advisable to have a minimum number of bases that is sufficient to cover the entire survey area without leaving 'dead' spaces (Fig. 10.19). In order to obtain the required accuracy in the determinations of the coordinates of points on the photographs of stereoscopic pairs and the horizontal parallax at each station, it is essential to establish a number of fiducial (correcting) points whose coordinates are determined by the photogrammetric or geodetic method. Thus, it is possible to compare the coordinates obtained by two independent methods and to check the ste~eophotogrammetric survey. Three correcting points are usually established for each photographed stereoscopic pair at each station. One of these points should be located in the closer plan and the other two, in the farther plan of the area being photographed. In order to decreasethe number of correcting points, some of them are usually made common for adjacent stereoscopic pairs. Places for establishing the photographic bases are chosen so that the bases can be ~llel to the working front and at the same level with the objects to be photographed (or somewhat above them). It is also essential that the height difference of the ends of the photographic basesbe as small as possible. In stereoscopic photographs of a quarry taken from an inclined base, the like points will be displaced relative to each other (vertical f)a-

10.2.

Reference

and Survey

Base3 (200 m) Base3a (BOm) ~

Nets and Surveying

Work

253

photographic bases can be located on the flanks of a quarry if the quarry depth is not large; in deep quarries, photographic bases Base2 (170m) ./1 \ are arranged on bench berms; Base2a (60 m) ./ .I;:-, ~ i 1/ .';Z:A'.-~ (2) in working systems with internal waste I ~, 'x::i .\',. \dumps and in those with conveyer bridges, I .1 ~' I ~// \ , .i" <." zee""7-:7'\ -.) photographic bases are located directly on ~ --' ,~ / /-r. \ ( \~ / the dumps; \ ---"t;..~:7 .\ (3) in combined working systems where Basel(80m) ...\ Base4(100m: \ rocks are transported to external and \ internal waste dumps, the upper and lower t;') \ I I H8 ~ benches are photographed separately. The 1 Base 5 (100 m) upper benches are photographed from the ~I "'1 ,.\ baseslocated on a non-working flank and the \ , .. lower ones, from the bases on internal waste \ Fiducial' ) points I dumps. To take photographs, tripods are set up at ~ the ends of a base. A theodolite is arranged on the left-hand end of a base (relative to the direction onto the objects to be photographed) in order to measure the length of the base line. After that, the photographic 100 0 100 200m camera is oriented relative to the base, and photographs are taken from the left-hand Fig. 10.19 Example ,of stereophotogrammetric and right-hand end of the base. The optical survey of quarry axis of the camera is arranged normally to rallax). This effect can be fully avoided or at the direction of the base line. least minimized to a tolerable level in a Geodetic work in ground stereophotostereocomparator only in cases when the grammetry includes the following operations: height difference between the ends of the I. Determination of the planimetric cophotographic base is not more than O.3Bph. ordinates of the left-hand points of basesand Besides,base points should be established in measurements of base lengths. The length of places where they can be preserved for a long a photographic base can be measured by a time. Adjacent bases should be chosen so as tape, wire or other instruments, provided that to ensure the specified overlap in adjacent the discrepancy between the forward and stereoscopic pairs. Places for the location of back measurements is not more than photographic bases should be chosen so that 1/5000-1/2000 of the base length. The plaa porti~~ of quarry or land can be photonimetric coordinates of the left-hand base graphed With the least possible number of points can be determined by triangulation, method of analytic network, by intersections stereoscopic pairs. Depending on the size of quarries, working and resections, polygonometric or theodolite systems, and the orientation of the mining traverses, polar method, and photogramfront, the following versions of the arrange- metry. ment of bases in quarries are possible: 2. Determination of a direction angle. The (1) in working systems with overburden direction angle (aB) of a photographic base is transportation to external waste dumps, found by measuring in the left-hand base

J

254

Ch. 10. Surveying

point of horizontal angles between the direction from that point onto the righthand point of the base and the direction formed by two certain points of a geodetic reference net. These angles are measured with an accuracy not worse than 5". The error in the measured direction angle of a base should be not more than: ma =

me

(101?) , ,

D

2yphmax

where p" = 206265" and meis the permissible root-mean square error in determining the positions of contour points. 3. Determination of the elevation marks of bases and correcting points by technical geometric levelling. The correcting points are fixed by placing marks on them, which are made as screensof plywood or another material. The vertical and horizontal sizes (b and a) of screens are calculated by the formulae: b = O.12yp h /j~, max

a = O.O6yPh

max

/fc

(10.13) Photography proper is a critical procedure in stereophotogrammetric surveys of quarries, since the quality of negatives produced is decisive for the accuracy with which the point coordinates and parallax will be detemlined. The best results are obtained on sunny cloudless days. During exposure, the Sun should be behind or sideways of a surveyor. On cloudy days, it should be observed that the objects being photographed are not shaded by clouds at the instant of exposure. Photographs are made on high-contrast repro-c duction films or plates. ~\ When making the photographic field work, the phototheodolite is set up on one of the base points so that two of its foot screws are arranged along the direction of a base line. A lifting apparatus with a sighting mark is established on the other base point; the foot screws of this apparatus should also be

in Quarries

oriented along the direction of a base line. Photographs are taken by the techniques including the following procedures: (I) tripods with lifting devices are set up on both points of a base line, and the elevation of the left-hand base point is measured; (2) the phototheodolite is then arranged on the left-hand point, and the sighting mark, on the right-hand point; (3) the phototheodolite is oriented onto the right-hand point of the base, and it is checked that the camera lens is closed; (4) a plate-holder (film-holder) is set in place, and its shutter is withdrawn; (5) the plate-holder is pressed against the focal frame of the camera by means of a screw on the back cover; the serial number of the photograph to be taken and the number of a station are set up on the numerator, and the kind of photograph (normal or with right- or left-hand deviation) is recorded; (6) the positions of spirit levels and the orientation of the phototheodolite are checked; (7) the correct exposure time is determined; (B) the plate is exposed, and the positions of spirit bubbles and phototheodolite orientation are checked again; (9) the holder shutter is closed, and the plate-holder is taken off from the camera; (10) new photographs are taken irl this way, with the camera axis shifted first to the left and then to the right; (II) the phototheodolite is taken off, and a sighting mark is set up in its place; and (12) the photo theodolite is set up on the right-hand base point to take new photographs as described. Stereophotogrammetric office work includes the processing of exposed plates (films) in a laboratory, preparatory work, and the compilation of the plans of mining workings. The preparatory work includes the following procedures: (a) calculation of the geodetic coordinates

10.2.

Reference

and

Survey

and elevations of base points and reference points; (b) preparation of the processing apparatus; and (c) preparation to the correction of a model. The results of the planimetric and elevation surveying of bases and correcting points are processed in the office by common geodetic methods. The most popular one is the graphometric method with the use of stereoautographs and other devices operating by the principle of photogrammetric intersections. These devices can solve mechanically the formulae for the normal and equi-deviated cases of photogrammetric survey. The coordinates of the points of a terrain are determined on stereophotographs by means of stereocomparators. The operating principle of a stereocomparator reduces to the reconstruction of the land portion photographed at a particular instant by constructing a geometrical model. Each point of the model is obtained by making intersections from the ends of the projection base. The planimetric coordinates of points, x and y, are found graphically in the stereoautograph and fixed by counters, in millimetres, on the scale of a model. The elevations of points are read off, in metres, from the altitude counter of the stereoautograph. By combining the stereoautograph with a plotting table (coordinatograph), it is possible to construct plans and profiles and deliver the planimetric and height coordinates of points onto a perforated tape or printer. Plotting a plan is started from drawing the elements of hydrography. After that, horizontals are plotted. In the plans of mountainous regions, plotting horizontals is started from the highest points. The results of the stereophotogrammetric survey of a quarry can be used for calculating the volume of mined rock. This can be done by using the measured photogrammetric co-

Nets

and

Surveying

Work

Zphi

al,

rph

ordinates of points of bench crests. Volumes are calculated by means of digital models or tables of positions of benches with their characteristic cross-sectional areas. If vertical sections are used (Fig. 10.20), the areas are calculated by the following formulae: a -" , a -" , ;,u-Yph;,u-Yph;.u' ;,I-Yph;,I-Yphi,1 a; = 0.5 (a;,u + ai,,) h 'i = Zi,u, -Z;,I' , h "; = Zi,u" -Z;,I " h=0.5

(h~+h'~ ,

,

),

S.=a.h. ,

,

,

256

Ch. 10. Surveying

oblique stereophotogrammetry, the optical axis of a camera is held at a specified angle to the vertical. The planimetric aerial stereophotogrammetry of quarries is carried out from specially equipped aeroplanes and helicopters controlled by an on-board electronic computer. This ensures automatically that the aircraft will follow very accurately the given survey route at the specified altitude. The computer also calculates the paths of turns and takes into descending and ascending air currents and the velocity and direction of wind. The equipment of an air-survey aircraft can control automatically the frequency of exposures. The brightness of the land surface is measured continuously by exposure meters, and the variations of the terrain relief are traced by locators. Since aerial photographs are taken from an appreciable altitude, aerophotogrammetric cameras are of the fixed-focus type, i. e. focussed at the infinity. Photographs are made mostly on a photographic film. A large number of photographs (up to 200-300) can be taken without recharging the camera. The size of photographs can be 18 cm x 18 cm or 30 cm x 30 cm. As may be seen from Fig. 10.21 which shows the scheme of taking an aerial photograph of a terrain, an aerial photograph is the central projection of the terrain with the projection centre in a point S. The distance fc along the perpendicular drawn from the projection centre S onto the plane of an aerial photograph is ,called the main focal distance (length) of an ~rial photographic camera. The point of intersection of that perpendicular with the plane of a photograph (point 0) is the main point of an aerial photograph. The vertical line SN is called the photographic altitude (or clearance) (H), and the point where this line intersects the plane of a photograph is called the photographic nadir. The angle OSN (a) is conventionally called the angle of inclination

in 01

Fig.

10.21

Taking

aerial

photograph

of terrain

of a photograph. If this angle is equal to zero, a photograph is called horizontal. A horizontal photograph of a flat horizontal terrain is virtually the plan of that terrain. The scale of a horizontal photograph is equal to the main scale, i. e. 1 : m = fc : H. Aerial photographs with the angle of inclination to the horizontal up to 3° are termed planimetric. With the inclination angles more than 3°, oblique, or perspective, aerial photographs are obtained. Before making an aerial photogrammetric survey, it is required to make calculations for selecting the survey parameters. For quarries with the rate of face advancement not more than 30 m, the recommended scale of an aerial photogrammetric survey is l/Ms = 1/10000; if the rate of face advancement exceeds 30 m, it is advisable to use the scale l/Ms = 1/15000. The selected values of l/Ms are then compared with its value calculated by the formula: ---

1.4m~

(10.14)

D Ms-(~). where

m~ =

0.02 mm

is the

root-mean

10.2.

Reference

and

Survey

Nets

and

Surveying

Maximum depth of quarry, m

fc, rnrn

up to 300 up to 200 200-300 300-500

100 100 140 200

'M,

'10000

Maximum depth of quarry, m

J;. mm

up to 300 100 300-400 140 400-500 200

square displacement of contour in plan expressed on the scale of a photograph; mv/v = 2.5% is the specified accuracy in determining the volume of extracted rock; and D is the width of a face. If it turns out that the survey scale calculated by formula (10.14) is larger than that adopted initially, the aerial survey should be carried out on a larger scale. The focal length fc of the aerial photographic camera for quarry surveying is chosen depending on the selected scale M. and the depth of the quarry by reference to Table 10.1 The photographic altitude H ph above the medium plane of the quarry is calculated by the formula: Hph = fcM. The photographed materials are processed in stereophotogrammetric apparatus with projector cameras similar to those used for taking photographs. The projector cameras and negatives are arranged mutually in the same positions they had at the instant of exposure. In this way there is formed a spatial model of the surveyed terrain on a reduced scale, which is analysed by means of a binocular microscope and spatial marks. For aerial surveys of quarries, a flight course for a photoairC!:alt should be plotted. For most quarries, a single course is usually sufficient. For those of an intricate configuration and large dimensions, a number of courses are plotted (Fig. 10.22). Aerial photographs taken along a course 17-1?70

257

""'

Table 10.1

15000 18000

Work

.x

v

Fig. 10.22 Making two courses of flight for aerial photography of quarry of intricate configuration

should have a longitudinal (forward) lap (Fig. 10.23)which is denoted by p and expressedas percentage of the side I of a photograph. The longitudinal lap can be calculated by the formula: h p = 62 + 50 ~

(10.15)

2Hph If parallel courses are plotted, the photographs of adjacent courses should have a lateral (side} lap q which is e~pressed as percentage of the photograph side length and calculated by the formula:

where 1 is the size of a photograph and m is its scale. An inclination angle of a photograph causes the displacements of points on it. For planimetric aerial photographs, it can be

Ch. 10. Surveying

Fig.

10.23

Longitudinal

and lateral

~ laps of photographs

taken approximately that the displacements take place in the direction of a line connecting a particular point with the main point of the photograph. Depending on the location of a point and the inclination angle of the photograph, this displacement can be directed towards the main point or away from it. The maximum displacement of a point in planimetric photographs under the effect of the inclination angle can be determined by the approximate formula (see Fig. 10.21): 8" = (r2/fc) (a/p) (10.18)

in Quarries

in courses

displacements on aerial photographs (Fig. 10.24). Introducing the designations: AAo = h is the height difference of a point A above a point N; SN = H is the photographic altitude; aO = r is the distance on an aerial photograph from a point a to the main point of a photograph 0; and aao = L\r is the displacement of a point on a photograph due -q-Qo

Q

~s

where r is the distance from the given point to the main point of a photograph; a is the inclination angle of a photograph; and p = 57.3!1. For instance, the maximum displacement of a point on a photograph withfc = 200 mm, r = 50 mm, and a = 2° will be: 8" = (502/200) (2/57.3) = 0.4 mm ~

It then follows that the displacements of points on aerial photographs under the effect of the inclination angle are mostly insignificant and in some cases can be neglected. Since the points of the physical surface of the Earth are located at different heights relative to a level surface, this oauses their different

AO

, Fig. 10.24?Determining on aerial photographs relief

" N displacements of points owing to the effect of land

10.2.

Reference

and

Survey

Nets

and

Surveying

259

Work

S1S2Ml' we have: H1 = Bphfc/P1

(10.20)

This expression can also be written for any other point on the terrain, say, M 2: H2 = Bp/c/P2 (10.21) Since the elevation difference of two points can be regarded as the difference of their distances, then: h=H2-H1

Fig. 10.25 to distance base

MO Longitudinal parallax and its relation from point on land to photographic

Noting expressions (10.20) and (10.21), we obtain: h= ~

-~

P2

= Bp/c(P1 -P2) P1

PtP2

Denoting (Pi -Pi+ J by Lip. we can finally write: to the terrain relief, it may be written that: Ar = rh/H (10.19)

h=~

Experience shows that the distortions in aerial photographs increase with increasing distance of points from the main point of a photograph. Thus, in operation with aerial photographs, it is advisable to utilize only the central portion of photographs, which is called the useful (working) area, rather than the entire area. Practically, the useful area of a photograph is limited by the lines drawn in the mid of the longitudinal and lateral lap. Photographs obtained by aerial stereophotogrammetry have a longitudinal lap more than 50%. Thus, each portion of a terrain is depicted on two photographs. Let the point M I of the terrain (Fig. 10.25) be represented by a point mI on the left-hand photograph and by a point m~ on the right-hand photograph. The distances from the photographic centres to these points are mI OI = xi on the left-hand photograph and m~O2 = -x.. on the right-hand on~)The difference xI -x.. = = PI is called the lon-gitudinal parallax. Considering similar triangles m~m~S2 and

On aerial photographs with an inclination angle or non-horizontal base, Pi and ~P turn out to be distorted. For that reason, before calculating the elevation differences, the values of Pi and ~P are corrected for the effect of the inclination angle and inclined base line. This problem can be solved analytically or with the use of photogrammetric devices. The observations and measurements on aerial photographs are made by a stereoscopic method. The simplest stereoscopic device is a stereoscope in which a left-hand photograph is mounted at the left and viewed by the left eye and the right-hand one is mounted at the right and viewed by the right eye. In this method, a direct stereoscopic effect is produced, i. e. points which are closer to an observer in nature will be seen closer in a stereomodel. Before the aerial surveys of a quarry, it is required to carry out field preparations. In particular, each stereoscopic pair should be provided with four points of planimetric and

17.

(10.22) Pi+

~p

260

Ch. 10. Surveying

elevation control (control points, or beacons), which are usually arranged in places where they can be preserved for a long time and used in subsequent aerial surveys. The planimetric coordinates of the control points should be determined with an accuracy specified for the coordinates of survey net points. The elevation marks of control points are determined with the accuracy of technical levelling. Aerial photographs are processed for the purpose of compilation and complementation of mining work plans. This is done in all-purpose stereophotogrammetric devices. Irrespective of the type of device, processing includes the preparatory work, mutual orientation of aerial photographs in the device, and geodetic orientation. The preparatory work includes the preparation of plates (application of kilometre network and control points), manufacture of transparencies, preparation of aerial photographs, checking of the device, calculation of model scale, focal lengths of cameras, etc. The mutual orientation of aerial photographs is essentially the determination of the position of one photograph in a stereo pair relative to the other. This procedure can be performed by various motions depending on the design of a particular device. For instance, one of the cameras may be considered to be fixed and forms a stationary basis relative to which the position of the other camera is measured. The mutual orientation in a stereophotogrammetric device is carried out by observing successively a number of points on photographs and eliminating their lateral parallax. Though the problem is solved by the method of successive approximations, the resulting solution is quite accurate (to the accuracy offered by the apparatus for the elimination of lateral parallax). The geodetic orientation of a geometrical model includes its scaling and horizontalization. The scaling consists in determining

in Quarries

the ratio of like line sections s and S taken respectively on the restored and photographed surfaces, i. e. l/m = s/S. In order to determine the scale of a model, at least two control points should be available. The horizontalization of the model reduces to determining the angles of turn of the model on the corresponding axes x and y of the geodetic system of coordinates. Thus, for solving the problem of geodetic orientation of the model, it is required to have at least three control points, all the coordinates being known for two of them and the elevation mark, for the third point. In geodetic orientation, the plate is also oriented. For this purpose, the measuring mark of the device is matched with one of reference points, and the centre of a focussing microscope is set up above the corresponding point on the plate. The microscope is then sighted onto another reference point, and the plate is turned until the centre of the microscope will be on the line connecting these points. 10.3.

Mine-Surveying of Drilling and Blasting

Coverage Work

Mine-surveying servicing (coverage) of drilling and blasting work consists in the following: (a) preparation of the initial materials for making a plan of blasting operations; (b) transfer of the blasting plan into nature; (c) determination of the actual positions of blasting holes after drilling; and (d) determination of the volume of blasted rock and the location of worked-out area after rock excavation. A plan of blasting operations is compiled on a scale of 1/1000 or 1/500. Surveys are carried out for the purpose, which have to determine the following characteristics: the position of the upper bench crest; boundaries of the slope fully cleared up by excavation;

10.3.

Mine-Surveying

boundaries of the muck pile left after earlier blasting work; elevations of the characteristic points of the upper and lower berms of a bench (in intervals not more than 20 m); positions of -line s and railway tracks (in quarries with railway transport); boundaries of rocks in the massif with different characteristics of drillability and explosibility; positions of tectonic disturbances and characteristics of cleavage cracks; boundaries of a dangerous zone as determined by the rules of blasting work and positions of buildings and structures near that zone. According to the plan of blasting operations, the design positions of the mouths of blasting holes are transferred into nature and fixed by pegs with marks indicating the number of a hole, the number of a drilling rig, the design depth of a hole, and the soil resistance. In laying out the hole mouths, the mine surveyor, as a rule, transfers instrumentally into nature only the boundaries of the block to be blasted and marks them on the upper crest of a bench. The mouths of blasting holes in a block are marked by a blaster foreman. The instrumental layout of the mouths of blasting holes is carried out only in cases when the portions to be blasted are located at the design boundary of a quarry and per" manent access roads are being built. The main methods for transferring blasting holes into nature are the polar method and method of perpendiculars with the use of points of a surveying net. Angles are laid off with an accuracy not worse than 5'. Distances up to 50 m can be measured by means of range finders. In the method of perpendiculars, measured distances are rounded off to a decimetre. If a quarry has high benches of an irregular shape, these should be surveyed properly. Since, according to safety regulations, staffmen are prohibited to stand on the slopes of benches, such slopes should be surveyed by

Coverage

of

Work

261

(a\

/

II " " "

/ / QJ 0.

~

/ 4 /

..,i~, " , ~

/

~I

I

~ (b)

't-:

Fig. 10.26 Surveying means of inclinometer; rod

of bench profile: (a) by (b) by means of telescopic

instruments which can determine the positions of staff points without the presence of men on them, for instance, tacheometers, inclinometers (or theodolites) with an attachment for measuring inclined distances, a telescopic rod with a tape, etc. For making a profile survey by an inclinometer (Fig. lO.26a), the instrument is set up on the upper crest of a bench to measure the inclination angle onto a characteristic point, after which the distance to the sighting point

262

Ch. 10. Surveying

is measured by a special tape. In order to measure a length, a cord with a weight is tied to the end of the tape and is let to slide along the slope of the bench. One of the workers stands on the upper crest and lowers the tape end with the weight, whereas another worker, standing on the bench foot in a safe place, stretches the cord and the tape so that the tape beginning is matched with the point to be measured. Measurements with a telescopic rod are made in the following manner (Fig. 10.26b). The telescopic rod with a roller at its end is applied horizontally to the crest and a measuring tape with a weight is ed over the roller to the point of interest on the slope. Two coordinates are measured: the horizontal distance from the upper crest to the rod end and (on the tape), the vertical distance from the rod end to the surface of the slope. After drilling the blasting holes, the block to be blasted should be surveyed. The positions of the holes at the flanks of the block are fixed from the points of a surveying. The positions of intermediate holes are determined by measuring the distances between the holes. Besides, it is required to measure the distances from the holes to the upper crest and the soil resistance. If the excavator work or clear-up work is carried out on the bench after compiling the plan of blasting operations, an additional survey of the bench should be carried out. The height marks of the mouths of blasting holes are determined by geometrical levelling. Having surveyed a prepared blasting block, the mine survey6r compiles cross sections through blasting holes on a scale of 1/500, 1/1000 or 1/2000, which are needed for making a corrected plan of blasting work. These sections should show the profile of the bench slope, blasting holes, the design and actual level of the bench foot, s of various rocks and mineral, and drillability and explosibility characteristics of the rocks. It is also required to draw a plan of the

in Quarries

blasting block which should give the block boundaries, blasting holes, the positions of the upper and lower bench crests, rock s, and the situation on the bench berms. Mter blasting, the blasted rock is surveyed in order to determine the boundaries of the muck pile, the break line, and several characteristic points along the profile lines on the surface of the muck pile. 10.4.

Survey Work Servicing

for

Transport

This work, which occupies an essential place in the daily activity of mine surveyors in quarries with railway transport, includes the laying out of routes of face railway tracks, periodic profiling of tracks, etc. In order to obtain initial data for laying out railway tracks, a levelling survey of the bench surface is done after the removal of the first strip of the rock from the muck pile. This survey determines the recessed places which should be filled with soil and the protruding ones which should be cut off for evening the berm. After that, the railway track axis is transferred onto the working berm of the bench. Two circumstances should be considered in this case: the axis should be laid out so that two bands of an excavator cut can be charged into cars without relaying the railway track, and the tracks should not occupy the zone of the muck pile of a next blast. As the design axis of the railway track is transferred into nature, picket points are established along it, and geometric or trigonometric levelling is carried out. By the results of levelling, it is decided to correct the track profile in accordance with the permissible ruling gradient. The surveys of permanent railway tracks in a quarry and beyond its boundaries are made by the method of perpendiculars or polar method from the sides of a theodolite traverse run along the track axis. These surveys have to determine: the axis of a track; centres

10.5.

Survey

Work

of switches; the top gauge width; the width of filling and grooves at the top and bottom; places for kilometre poles; etc. Track curves are surveyed by the method of perpendiculars: chords are drawn between the ends of a curve and distances to the axis of the curve are measured along perpendiculars to these chords. The layout work for the construction of automobile roads is carried out by mine surveyors according to the design materials which give the gradients, curvature radii, width of roadbed, etc. At the end of road construction, instrumental survey should be carried out in order to check that the actual characteristics of the road correspond properly to the design values. 10.5.

Survey

Work

in Trenching

This work is carried out on the basis of design materials which should include: the plan of a trench with the coordinates of junction points, direction angles of junctions, angles of turn, distances between the vertexes of turning angles and radii of connecting curves; longitudinal and transverse sections of a trench which should show the profiles of the Earth's surface and the design profile of the trench bottom, the sequence, cross sections and axes of cuts, and railway and drainage ditches; the plan of blasting holes with the coordinates of their mouths, direction angles of hole axes, and hole cross sections. For laying out a trench on the ground, a theodolite traverse is run. The positions of upper crests (for trenches to be cut in loose rocks) or the positions of blasting holes (for those to be made in hard rocks) are transferred into nature from the sides of that traverse. In making trenches by power shovels without blasting work, the following cases of mine-surveying servicing are possible: 1. A trench is dug in a slope and the extracted rock is dumped downhill

in

263

Trenching

30

-3~=--3'{,1-

!':-

cT

1~~

64

~o

93

"

O

4'

.

J~

~ ~

O 40

~/'lc

1?0 ~2 I,

~2 .-A

~ "

..A

" 8 8

Fig. 10.27 Trench digging in slope (Fig. 10.27). The main task of the mine surveyor in this caseis to observe that the trench axis has a specified gradient. Initially, the junction point 1 of the trench axis is transferred onto the ground according to the design coordinates. A theodolite traverse is then run according to the preliminary direction of the trench axis. This direction is fixed by temporary picket points in intervals of 50-100 m. With the known points of the trench bottom, points 10' 20, 30, 40 are determined in nature; these points form the line along which the plane of the trench bottom intersects the slope. After that, the corrected trench axis is laid out (points 1, 2, 3, 4) by using the intersection line and the design width of the trench. Finally, the lines of the upper crest (points 1", 2",3", 4") and of the lower crest (points 2' and 3') are marked

264

Ch. 10. Surveying in Quarries c-c

1°°° i 0 0

0

1 00°°'0

1000 C -.1-0

072

'/\I'fi~~r# \ I III

0001 I

I'

-0-0-

~-0-o-0-'--

I...

I/

\JrLI-~1

c

...1

1...t..~1 1...t...1 B : ... -+

! ...I

IB

~.~-81A-A

y

>---r ~

A

Fig.

Fig. 10.28 Trench cutting with continuous and rock loading into railway cars

iJ7

10.29

Trenching

by excavating

explosions

face

on the ground by measuring from the trench axls. 2. A trench is cut in a continuous face and the extracted rock is loaded into transport vehicles on the trench flank (Fig. 10.28)or the rock is extracted by drag line and discharged onto the trench sides. A theodolite traverse is run as described in the previous example. The trench axis AB is transferred and fixed in straight portions at distances up to 50 m and in curved portions at intervals up to 10 m. At the same time, the axis of the railway track is laid out on the trench flank (or the axis of the waste rock dump if the trench is dug by a drag line). During the cutting of the trench, bench marks are established in intervals of 20-30 m (R1,R2, R3, etc.) which give the elevations of the trench foot. The bench marks should be displaced from the trench axis so as to be on the line of one of excavator tracks.

3. A trench is made by excavating explosions (Fig. 10.29). In this case, the design positions 2 of the blasting holes are transferred into nature by means of theodolite traverses or geodetic intersections. After drilling 'the blasting holes 1, they are surveyed for the correction of the plan of explosions. Mter blasting, another survey is done to determine the volume of blasted rock: then the axis and side crests of the trench are transferred into nature, and bench marks are established to control the trench foot gradient. 10.6.

Survey Work in Open-Cast with Conveyer

Mining Bridges

The specifics of survey work in this case are associated with the fact that conveyer bridges have a rather intricate design and a very larg~ mass (sometimes more than 7000 t) (Fig. 10.30), that is why high dynamic loads that may cause overstressing the bridge el-

10.6.

Survey

Fig. 10.30 Conveyer bridge: I-facing ; 5- dumping console truss

Work

console

in Open-Cast

truss; 2-facing

ements are inissible. This necessitates additional survey observations on the trusses and other e,lements of conveyer bridges in order to preserve their strength. The minesurvey servicing of conveyer bridges consists in checking the plan position and gradients of the railway tracks of bridges and controlling the horizontal, vertical and angular mobility of a bridge. The plan position of tracks is controlled by theodolite surveying with measuring the spacings between the rail lines by a steel tape; the track gradient is controlled by geometric levelling. The control of horizontal mobility is carried out in view of the fact that the distance between the facing and dumping s of a conveyer bridge can be increased or decreased depending on the varying geometry of faces.An increase or decrease of this spacing beyond the specified limits is however inissible. The mine surveyor has to control periodically the spacings between the axes of the facing and dumping s. For this purpose, theodolite traverses are run along or near the track axes on the working berms of benches on which the bridge s are moving. The theodolite traverses should always be connected to the points of a reference net. A series of profile lines roughly perpendicular to the mining front are also laid out in a quarry. In each profile, the distances from the sides of the theodolite traverse to

Mining

;

265

3-middle

truss; 4-dumping

the nearest rail are measured by the method of perpendiculars and recalculated into the distances to the axes. By the results of field measurements, the positions of axes are marked on the mine-surveying plan which serves as the basis for correcting the positions of tracks and s of a conveyer bridge. The control of vertical mobility of conveyer bridges is done to check that the height difference between the s of a bridge does not exceed the specified safety licnit. The detailed surveys of coQveyer bridges are carried out for determining their deformations in order to prevent the appearance of dangerous deformation. This work requires the stoppage of a bridge for a long time. In these surveys, points are marked at the intersections of beam axes in each unit of the metal structure of a bridge. The axial line bb' (Fig. 10.31) is fixed at the upper and lower horizontal belts of the bridge. A theodolite is then set up at the edge of the upper belt above a point 19-b', and the directions onto a point lI-b (longitudinal axis of the belt) and points 19-a' and 19-c' are determined. In order to determine the lateral deformations of the bridge truss, the ordinates from the axial lines to the centres of units of metal structures are measured by a millimetregraduated rule or ordinatometer arranged perpendicular to the collimation axis of the

266

Ch. 10. Surveying

in Ouarries

Top cho

~

a' ***~~1918171615141312

A

1110

9

876

54

3210111a

Axis b'

--c -b

c'

Bottom a,19181716151413

12All

10

chord 9876543210111111

.

~.

~

~~~=a ---b

.c c

Fig.

10.31

Fixation

of axial lines of conveyer

bridge for detailed

theodolite. The distances between the points along the collimation axis of the theodolite are measured by a controlled-tension steel tape. Similarly, the distances in cross sections to the extreme points of the belt are determined. The results thus obtained are used for plotting the actual state of the bridge on the design plan and listing the deformations of all units of the upper belt of the main truss. The horizontal surveying of the lower belt of the main truss is carried out by the method of ordinates from the sides of a theodolite traverse run on side ladders along the truss. Measurements are made by controlled-tension steel tapes with an accuracy to a millimetre. A plan of the lower belt is plotted by the results of a survey, and the actual positions of structures are marked on it.

10.7. Calculations of Volumes of Extracted Overburden Rock and Mineral in Quarries In mine surveying, the volumes of extracted mineral and overburden rock are calculated by the main plans of mining work levels. The choice of the best calculation method depends on the mining technology and the surveying method employed. I. In open-cast mining of loose rocks by conveyer bridges, excavators, etc. the work-

surveys

ed-out area has a more or less regular shape, and the required accuracy in calculations of the volumes of excavator cuts can be ensured by any method of surveying, including tacheometry. 2. On some kinds of loose deposits, the worked-out area has an irregular shape, so that tacheometry cannot ensure the specified accuracy. In such casesit is recommended to employ the ground stereophotogrammetric surveymg. 3. In the extraction of igneous and hard ro9ks with preliminary loosening to the width of one excavator cut, the calculations of volumes should be carried out by the results of ground stereophotogrammetric surveys or by weighing the mined rock and considering its density. 4. If rocks are loosened by multirow blasting and the loosened rock is later loaded by several excavators, the calculations of volumes can only be done by the results of weighing of the mined rock (of the known density), since other methods are insufficiently accurate. The determination of volumes by the results of weighing of the mined rock (operative ing) has a number of essential advantages: (a) the method offers the highest accuracy and can be used with all technological schemes of mining;

10.7.

Calculations

of Volumes

(b) it provides timely information on the volumes of mining and stripping work even for individual mining teams and for any time interval; and (c) it is possible to control efficiently how fully the transport vehicles are loaded. The volumes of extracted and blasted overburden rock and mineral can be calculated by the method of arithmetic mean, horizontal and vertical sections, volumetric measuring grid, etc., provided that the 'errors in their determination do not exceed the following permissible values. 1. If the volume of the extracted overburden (mineral) is found directly by surveying of benches, the permissible error cry, %, can be calculated by the formula: p cry

=

1500/JV

(10.23)

p

where V is the volume of the extracted rock (recalculated to the undisturbed rock), m3. Formula (10.23) is applicable for volumes from 20000 m3 to 2000000 m3. For larger volumes, it may be taken that cry = 1%; for smaller volumes, the method of surveying and calculatiO;n of volumes is established by an instruction so that the error cry is not p greater than 10%. 2. If the volumes of the extracted (blasted) overburden rock and mineral are determined in the loosened state and recalculated to the volume of the undisturbed rock (using the loosening factor), the permissible error cry, p %,

can

cry

=

be

found

2200/JV

by

the

formula:

(10.24)

p

where V is the volume of the extracted (blasted) rock recalculated to that of the undisturbed rock, m3. Formula (10.24) is applicable for volumes ranging from 45000 m3 to 2200000 m3. For greater volumes, it is taken that cry = 1.5% p and for volumes smaller than 45000 m3, the method of surveying and volume calculation and the determination of the loosening factor

of Rock and Mineral

267

are established by an instruction so that the error ay is not greater than IO%. The ~thod of arithmetic mean is recommended for cases when the mining technology permits the determination of the volumes of the mined rock (recalculated to the undisturbed rock) directly by the results of bench surveying. The volume of a block is calculated in that case by the formula: v= Shm where S is the area of the base of a figure or section, m2, and hm is the mean depth of a cut, m, or by the formula: V=~S!h2

m

where Su and SI are the cross-sectional areas at the upper and lower bench crests, m2, and hm is the mean depth of a cut, m. The mean depth of a cut can be found by the formula: hm= 1: 2u/nu-1: 2l/nl where 1: 2uand 1: 21are the sums of elevations respectively at the upper and lower bench crests and nu and nl are the numbers of staff points on these crests. The method of horizontal sections is advisable in cases when bench crests and intermediate sections are indicated on the plan of mining workings. This is usually done by stereophotogrammetric surveying. In this method, the total volume is calculated as the sum of volumes of individual horizontal layers. The areas of horizontal sections are measured by a planimeter or measuring grid or determined analytically. Planimetry is carried out twice, following the contours of sections clockwise and counterclockwise. The discrepancy between the two measurements should not exceed 3% for areas up to 15 cm2 or 2% for larger ones. The final result is taken as the arithmetic mean of the two measurements. Large areas and sections of a regular shape

268

Ch. 10. Surveying 2 ..!:.Q.

~\

~: s

-/\\\1:,\

. n

'\. \

can be divided into simple geometrical figures whose elements are measured by a rnillimetre-graduated rule. Analytical determination of areas is also possible. The method of vertical sections (Fig. 10.32) is usually employed for calculating the volumes of blasted rock surveyed by tacheometric methods. The following formulae are used in calculations: (I) in cases when spacings between the section planes are different: SI + S2l

S2 + S3 2

l2

S.-1

-..on +Sn. ~ln-l

I +

+

tlU.L:»

where s 1 and S. are the cross-sectional areas at the boundaries of an extracted cut (block), m2; S2' S3' ..., S.-1 are the areas of intermediate sections, m2; and 11,12, 13' ...,1.-1 are the spacings between the sections, m; (2) "in case of equal spacings between the

) \

.I.

volumes of blasted rock if this is shown on a plan in projections with numerical marks or in cases when a cut has intricate contours and surface. The volume of the rock in this method is found by the formula: n

v

Fig. 10.32 Determining mineral reserves by vertical sections

v- -2

in Quarries

2

where I is the spacing between the sections, m; S are the areas of intermediate sections, m2; and n is the number of sections. The spacings between the sections should be not greater than the distances between the staff points. The method of volumetric measuring grid is recommended for the calculations of the

sLh, 1

where S is the area of the grid base, m 2; n is the number of baseswithin the boundaries of the contour being measured; and h is the thickness of the layer of extracted (blasted) rock in the centre of each grid base. The choice of a method for volume calculation depends on the shape of the worked-out area and muck pile, as well as on the method of surveying. In surveying of undisturbed rock, various methods can be used for the calculations of volumes. With a tacheometric survey which determines the positions of bench crests, the method of horizontal sections is preferable. With tacheometric surveys carried out once a month, area measurements should be done plans plotted on a scale not smaller than .1/1000. If calculations are done once a quarter of a year, plans on a scale 1/2000 can be used. If surveying is done by ground stereophotogrammetry, rock volumes can be calculated by the method of horizontal or that of vertical sections. In the former case, areas are measured by a planimeter. In the method of vertical sections, areas can be determined by analytical or graphoanalytical methods. surveys of mined rock a muck pile byIna the tacheometric method, theinvolumes can be calculated by the method of vertical sections; if the muck pile is surveyed by stereophotogrammetry, the method of vertical and that of horizontal sections are applicable. Recalculation from the volume of loosened rock to that of undisturbed rock is done by dividing the measured volume by a loosening factor.

10.8.

Reclamation

The calculations of the volume of a muck pile produced by multirow blasting can involve certain difficulties, since the loosening factor of rock may vary within rather wide limits (its average variation may attain 8% or even more). In such cases,the calculations of blasted rock and the determination of a loosening factor should be carried out separately for each block before and after blasting. for blocks exploded onto a cleared-up slope, the mean loosening factor can be found by the formula: k, = ~/V.n where ~ is the volume of a block in the loosened state and ~n is the volume of undisturbed rock in a block. If blasting is done onto an uncleared slope, the volume of undisturbed rock in the blasted block should be summed with the volume of the blasted rock left on the slope from the previous blasting; the loosening factor of this rock is taken such as adopted for the calculations of the volumes of the last extracted cuts. Thus, the mean loosening factor is calculated by the formula: k. = ~/V' where J-;is the volume of the loosened rock; V~. = v.. + V~, (here v.. is the volume of the undisturbed rock in the block and V~l is the volume of the blasted rock remained from the previous blasting, recalculated to the volume of the undisturbed rock). By the resl,llts of surveying before and after the extraction of the first excavator cut, it is possible to calculate the volume of that cut and the mass of rock in it and in the remaining portion of the blasted rock. The volume of the undisturbed rock in the first cut can be found by the formula: V~. = V;/k; where V; is the volume of rock of the first cut in the loosened state and k; is the mean

of

269

Land

loosening factor for the first cut, which should be determined experimentally. In the calculation of the volume of the first cut of a block, a correction (with a plus sign) for the generalization of the slope shape is introduced: AV= (O.O3h3+ O.7h)L where h is the mean height of a slope and L is the length of a block. The volumes of subsequent cuts are calculated without this correction. The loosening factors for the subsequent cuts are determined by considering the factor for the first cut, the mean loosening factor of the block, and the areas of corresponding vertical sections of the first cut and the remaining portion of the block: V"

= V"

un

,

/

k" 1

k'1 -kl (P' + pI') + k;P' , -11 p where k7 is the loosening factor of the second and subsequent cuts in a block; k, is the mean loosening factor of the rock; k; is the loosening factor of the rock in the fJ.fstcut, and p' and p" are the weights of the loosening factors, which are taken equal numerically to the mean areas of vertical sections in the first and subsequent cuts. 10.8.

Reclamation

of Land

The problem of the restoration of land areas spoiled by opell-cast mining of mineral deposits is of crucial importance. A complex of measures aimed at the restoration of land on the territories abandoned on opell-cast mining is called land reclamalion. Land reclamation can be carried out by engineering, biological and construction techmques. A mining enterprise should carry ellgin" eering reclamation which consists in the preparation of land territories. freed after

270

Ch. 10. Surveying

in Quarries

The design position of workings on the terrain is usually determined by the polar method from control points or by tape measurements from the nearest exploring workings whose mouths are shown on the plans of mining workings. The elements of layout work are determined graphically on plans plotted on a scale 1/1000 or 1/2000. The positions of workings relative to the surveying net points should be determined on the plan with an accuracy not worse than 1.6 m. Elevation marks should be determined with an accuracy to 0.3 m in valleys with a weakly expressed thalweg (valley floor) or to 0.5 of the vertical contour interval in those with a pronounced thalweg. The main objects of mine-survey servicing in open-cast mining of placer deposits are as follows: the determination of the volumes of 10.9. Survey Work in Open-Cast the mining work performed, control of the Mining of Placer Deposits mining work and of the completeness of sand Placer deposits with the bedding depth up extraction. For these purposes, mine surveyto 15 m are worked out, as a rule, by ors fix on the ground the design contours of open-cast mining. Open-cast workings for- polygons, hydraulic sections, waste dumps, med by mechanization means (bulldozer- berms, access roads, and working platforms scraper complexes or excavators) are called for excavating machines; make the surveys of polygons if their depth is substantially smaller pqlygons or pits and determine the volumes than the width; deep and narrow workings of stripped turfs and washed sands and mined are called pits. Valley placers are often mined rock; control the thickness of stripped and undisturbed turfs and the depth of mining; by dredges. In open-cast mining of placer deposits, complement mine-surveying plans and secreference nets are usually developed at the tions; determine the reserves,losses and diluperiod of detailed prospecting so as to pro- tion of sands; and compile the documents on vide basis for surveys on a scale 1/2000. In the volumes of stripped and transferred sands regions not covered by a national reference and of mined and washed sands. net, individual reference nets can be estabThe following methods of surveying are lished by triangulation or trigonometry. Sur- mainly employed in open-cast mining of veying nets are developed according to the placer deposits: surface levelling by a rectanrequirements for land surveys. The points of gular network, ground stereophotogrammea surveying net should be established beyond try, tacheometry, and surveys by profile lines. the contours of a placer deposit. At least Surface levelling by a rectangular network three or four permanent points should be is used for surveying of polygons on perprovided per kilometre of the length of a mafrost placers which are worked out layerdeposit, and these points should lie at distan:- wise with an average thickness of layers 0.5ces not more than 150-200 m from exploring 1.5 m. The surface of polygons is levelled and mining workings. before the beginning of the mining work and open-castmining, for biological or construction cultivation. Engineering reclamation includes the following operations: preservation of the upper (vegetable) soil layer, levelling of dumps, construction of drainage networks, chemical melioration of the soil composition, for instance, chalking of acid soils (when required), and covering the levelled surface with a layer of fertile soil. The minesurveying service of a mining enterprise participates in the engineering reclamation of land. Mine surveyors have to observe that the upper soil layer is removed properly from the territory of future quarries and dumps, to control the levelling of worked-out areas and dumps and the covering of prepared areas with fertile soil.

10.9.

Survey

Work

in Open-Cast

Mining

of Placer

Deposits

271

at the end of each planned period. The by the points of the upper unflooded crests of contours of polygons and sections at the slopes in a polygon with a smooth surface upper and lower crest are usually surveyed by relief where there is the required number of the polar method from the points of survey surveying net points and control points. The control. distances between the surveyed points and Ground stereophotogrammetry is employ- pickets or control points are measured by ed for surveying of large polygons when an tapes. area of at least 25 000 m2 can be photoTacheometric surveying has found appligraphed from a single photographic base. cation in all main regions of dredging work. Tacheometry and method of profile lines In this method, the line of a lower crest is have found use for surveying of pits and also fixed upon determining the combination of of polygons which are deepened by more points of the largest depths at the foot of a than 1.5 m monthly, i. e. when a placer de- facing slope. With depths more than 2 m, the posit is being mined by excavators or hyd- positions of the crests of the facing slope is, as raulic machines actually to the entire depth a rule, determined by the position of the of bedding of loose deposits. The techniques centre of the lower bucket drum as it moves of tacheometric surveying on placer deposits over the facing platform. are the same as elsewhere. Range lines which On some placer deposits, tacheometric are parallel to one another are laid out across surveying is used only for determining the the strike of a pit. position of the upper crest of a facing slope. In the method of profile lines, the upper The position of the lower crest is drawn on and lower crests of the side slopes of a pit are the plans of the mining work relative to that first surveyed and plotted on the plan of the of the upper crest considering the specified mining work, after which transverse vertical slope angle, which is determined experimensections are marked with intervals of tally for different depths and lithologic cha20-25 m, the depths in the equidistant points racteristics of loose placer deposits. This of each section are measured, and a sketch of method is applicable only in rare caseswhen measurements .is drawn. the flanks of a dredge pit are composed of The survey work in dredging consists es- rocks quite resistant to caving, so that the sentially in surveying of dredge faces and pits, face retains its initial configuration during the determination of the volume of mined rock entire period between measurements. The mean depth of a dredge face is found and losses, and the dilution of the mineral. The periodicity of face surveying is determi- by averaging the measured face depths (depth ned by the accuracy of measurement of the of digging plus the height of freeboard) or by geometric parameters of dredge pits (poly- averaging the differences of elevation marks gons). For instance, for dredges of moderate of the polygon surface in the upper crest capacity, each third or fifth face should be contour and the bottom of the dredge pit. surveyed, i. e. roughly after every 10 m of The depth of digging can be measured by a dredge advancement. lead-and-line, mechanical depth gauge, echo Surveying of dredge pits can be performed sounder or asdic (sonar). The error in depth by one of the following methods. measurements should not exceed 0.1 m. With the linear method, surveying is done

Chapter Rock

11.1.

Introductory

Disturbance of Surface

Notes

Underground voids and cavities left on mineral extraction can impair the stability of enclosing rock and result in the disturbance (displacements) of the rock massif and the subsidence of the Earth's surface. Examples of destruction of underground and surface structures under the effect of rock disturbance are quite numerous. Rock displacements attracted miners' attention from the earliest times. In Liege (Belgium), already in the lSth century, colliery owners were obliged by the local law to mine coal at depths not less than 100 m in order to minimize the harmful effect of rock disturbance on municipal buildings. The scientific studies of the process of rock disturbance under the effect of underground workings were started in the first half of the 19th century when hypotheses were proposed to explain the laws of rock displacement. In 1838, Toilliez expressed an idea that rock layers above a stopiIig space destroyed along the planes perpendicular to the bedding plane. This idea was utilized by Gonot of Belgium for explaining the destruction of buildings in Liege. Later, these ideas were generalized into a hypothesis which was called the 'rule of normals' and reduced to the following. The mass of a portion C 1 of the roof above the worked-out space (Fig. 11.1), denoted by Q, has two pressure components: N which is normal to the bedding plane and T which is directed along that plane. Assuming that the

Eleven and Protection Structures

force T is counterbalanced by the reaction of the rock under the worked-out space, the motion of the same portion (layer) C 1 above the worked-out space (i. e. displacement of the roof) will take place only under the effect of the normal component. The same reasoning is true of the overlying layers C2' C3' etc. It then follows that the fracture of the roof rock layers above the worked-out space should occur at the upper and lower boundary of the stoping working and propagate along the normals to the bedding plane. Thus, the displacement angles in this case are 13= 90° -a and y = 90° + a, where a is the angle of dip of a seam. In 1867, J. von Sparre developed further the hypothesis of normals, but he supposed that displacement took place due to the fracture in dangerous sections where the

Fig.

11.1

Scheme

explaining

the 'rule

nonnal

11.1.

Introductory

bending moment was at the maximum. Considering rock layers as beams built in into the rock massif at both ends, Sparre derived the formula for the length of a span along which the displacement (fracture) of a rock layer should occur: 1= J2kd/D cos a where 1 is the length of a span; k is the bending strength of rock; d is the thickness of the rock layer; D is the mass of the rock layer; and a is the angle of dip of a seam. Sparre supposed also that rock displacement should occur not along the normals to a seam, but along the lines somewhere between the normals and verticals. Thus, the dangerous section in the lower portion of the roof should protrude, as it were, from the rock and that in the upper section should through the roof rock (Fig. 11.2). In 1882, F. Rziha suggested the hypothesis of rock displacement according to which the caving surface of a roof could be likened to a paraboloid (Fig. 11.3). As caving proceeds, the volume of the rock involved into displacement increases. Caving (displacement) comes to an end when the angle a of the lines 18-1270

273

Notes

confining the subsidence zone relative to the horizontal becomes equal to the angle of repose of 1he rock. In 1885, H. Fayol published a work which confirmed Rziha's hypothesis. According to Fayol, rock displacement occurs by the caving mode and involves a zone having the shape of a cupola (dome). By Fayol's assumption, the dome retains its stability even when its end s have collapsed; this is due to filling of the dome space by caved-in rock. By Fayol's reckoning, the loosening factor of the caved-in rock is equal to 1/200. Thus, with the depth of the mining work equal to 200 m (where m is the thickness of a seam) the extraction of a seam should have no effect on the surface. In 1864, J. Goodwin, a British scientist, carried out instrumental observations of SUfface subsidence on coal fields and determined the displacement angles ~ depending on the angle of dip a: Angle of dip a, 0

10 15 20

Displacement angle13,° ..73

24 27 31 40

71 70.5 70 68 67 64

In his experiments, the displacement angle 'Y was always equal to 83-85°. In 1895-97, R. Hausse proposed another hypothesis of rock displacement according to which the mechanical properties of rocks and their alternation played an essential part in the process. He also emphasized the effect of

Fig.

11.3

Scheme

to

Rziha's

hypothesis

274

Ch

a Fig.

11.4

Scheme

Rock Disturbance

and Protection

of Structures

b depicting

Hausse's

hypothesis

working systems on the pattern of rock displacement. According to Hausse, the process of rock displacement can be represented as follows (Fig. 11.4). A zone abdc forms immediately above the worked-out space,in which rock is displaced by caving and bending. Above that zone, there is another zone, dcef, where only the bending of rock layers is observed. The thickness of the cave-in zone was found to be equal to (30-60) m, where m is the thickness of the mined seam. A large contribution to the advancement of the theory of rock displacement was made by A. Goldreich in 1913 when he published a monograph based on his instrumental observations of rock subsidence. He came to a conclusion that the fault fissures in rocks of the coal age should have directions governed by the bisector rule (Fig. 11.5), i. e. the displacement boundary is a line coincident with the bisector of an angle between the normal to a seam and the vertical. For tertiary rocks, it was proposed to determine the angles of displacement by considering the angle of repose e = 45° + p/2 where p is the angle of repose. Further, Goldreich was one of the first to refer to the horizontal displacements of rocks. In recent time, the studies of rock sub-

Fig.

11.5

Scheme

of bisector

rule

sidence have been carried out extensively and on a wider scope and have included the problems of the pressure of rocks and filling materials, specific effects of rock pressure in mines with powered s, laws of rock pressure in ore deposits. Recent investigations of the mechanism of such dangerous effects as rock, coal and gas bursts carried out in a number of countries have provided the basis for developing effective measures to prevent the dynamic effects of rock pressure. 11.2.

General on Rock

Data Disturbance

The stressed state that appears after the formation of a cavity in the rock massif (say, upon driving a working) is determined by initial stress fields. The magnitude and distribution of stressesdepend substantially on the shape of workings. At the initial period when a stope working still has not been advanced far from the rock massif, the roof of a deposit is in a relatively stable state, and its bending is insignificant. As however the worked-out space is widened, the amount and rate of roof bending increase, the continuity of rock layers is disturbed, they are stratified, fissures form in the rock, and finally, roof layers cave in into the worked-out space. With an increase of the dimensions of the

11.3.

(a)

Rock

Displacement

Parameters

275

According to natural observations, the thickness of the cave-in zone along the normal to a seam in most coal basins does not exceed three- or four-fold thickness of the seam. The bend zone II which can be observed both in the overlying roof and underlying bedrock. Rock deformations in this zone occur by the separation of the bent layer into strata, though the bonds between the individual blocks remain undisturbed. Two portions are distinguished in the bend zone: a fissured portion just above the zone of complete caving and the portion above it where (b) Fall.through bending takes place without fissuring of the rock. The zone of bearing pressure III which can --~~-~1-~=~7 , ., \ form in the rock massif near the boundaries , , , of a stope working. Bearing pressure appears in places near a driven working where the ~(', overlying rock massif becomes uned, hangs up, and its weight is redistributed onto the enclosing rock of the working. The size Fig. 11.6 Pattern of rock displacement around and pattern of the bearing pressure zone in stope working: (a) with gently dipping bedding; (b) with steep dipping of seam the overburden rock depend on the extent of rock hanging at the boundaries of workings, the depth of the mining work, and rock worked-out space, the zone of rock defor- properties. mations, or displacement zone, becomes larThe zone of total displacementIV which can ger. At a certain ratio of the dimensions of form both at the surface and in the rock the worked-out space and the depth of the mass. It is assumed conventionally that the mining work, the displacement zone reaches stressed state in this zone is close to the the Earth's surface. gravitational state. In the general case, the following zones of In working of thick steeply dipping coal rock deformation around a stope working seams, the rock at the )ying wall often slides can be distinguished (Fig. 11.6): down and forms fall-throughs on the surface The cave-in zone I which is formed im- above seam outcrops. mediately at the worked-out space. Here, rock layers separate from the massif, disin11.3. Rock Displacement tegrate into blocks, and fall into the workedParameters out space. The thickness of the cave-in zone depends mainly on the ratio of thicknesses of An area of the ground surface affected by rock layers in the roof and seam of extracted the displacement from the mining work is mineral, the strength of the roof rock, the called a displacement trough, or basin. It working system employed, and the angle of usually appears as a plate- or trough-like dip of the seam. (seldom cup-shaped) depression of the IS.

Ch. 11. Rock

Disturbance

Earth's surface. Of particular interest are the vertical sections through a displacement trough in which the trough ends are at the farthest distance from the boundaries of a working. These sections usually through the centre of a trough on and across the strike and are called the main sections of a displacement trough. The displacements and deformations of the Earth's surface within a trough are distributed non-uniformly. A portion of the displa;, cement trough where the deformations of the ground are such that can cause damage to surface structures is called the hazardous displacement zone. Hazardous displacement zones are defined on the Earth's surface by using displacement angles which are meant as the exterior angles relative to the worked-out space,formed in the main vertical sections of the displacement trough on and across the strike by horizontal lines and by lines connecting the boundaries of the worked-out space with the boundaries of critical surface deformations. Displacement angles are determined from the conditions of complete underworking. This is understood as the state of the trough bottom in which further expansion of the area being worked out does not increase the displacement in this portion of the trough. Not all deformations appearing on surface subsidence are dangerous for the objects being underworked. The highest deformations of the Earth's surface which still cause no damage to surface structures are called the critical, or ultimate safe, deformations of surface. Though the critical deformations for various structures are different, experience shows however that for the majority of structures the following levels of critical deformations can be taken: 4 x 10-3 for inclination, 0.2 x 10-3 for curvature, and 2 x 10-3 for expansion. It is distinguished between the displacement angles in bedrocks and sedimentary rocks. For bedrocks, in sections across the strike, the displacement

and Protection

of Structures

(a)

Fig. 11.7 Displacement angles in section across strike: (a) with gently dipping bedding; (b) with steeply dipping seam

angles in the hanging wall at the lower boundary of the worked-out space are denoted by ~ and at the upper boundary, by y (Fig. 11.7a).For steeply dipping bedding, the dangerous zone is determined from the lower boundary of the worked-out space by the displacement angle ~ in the hanging wall and by the angle ~1 in the lying wall (Fig. 11.7b). In sections on the strike, the displacement angles are taken to be the same at both sides of the worked-out space and denoted by O (Fig. 11.8).For sedimentary rocks, the displacement angles are the same in all three ~irections and denoted by

Fig. 11.8 strike

Displacement

angles

in

section

on

11.3.

Rock

Displacement

(a)

Parameters

277

ibt

Fig. 11.9 Boundary angles for seams: (a) gently dipping ((J-angle of maximum subsidence); (b) steep

boundary points, i. e. the points on the Earth's surface in which subsidence does not exceedthe mean error of levelling. In practice, the boundaries of a displacement trough are defined by points with a subsidence of 15 mm or relative horizontal tensile deformations 0.5 x 10-3. It is distinguished between the boundary angles in sections across the strike ([30' [301' and y ° in Fig. 11.9) and those in sections on the strike (00). Boundary angles depend substantially on the depth of the mining work, dipping angle of seams, and, rock density. Boundary angles are used in preliminary calculations of displacements and deformations of the Earth's surface. With the horizontal bedding of a seam, the centre of a displacement trough lies above the middle of the worked-out space. With dipping seams,it is shifted from the middle by an angle e (Fig. 11.9a) which is called the angle of maximum subsidence. This angle is measured at the dipping end of a seam in the vertical main section of the displacement trough across the strike and is formed by a horizontal line and the line connecting the middle of the working with the point on the surface having the maximum subsidence or with the middle of a plate-shaped displacement trough. If the dimensions of the worked-out space are large relative to the bedding depth, the

Earth's surface may subside to the same depth (maximum for the given conditions) over a large area. Further expansion of the working will not increase the subsidence area, and the latter is then considered to be under the conditions of complete underworking. Otherwise, underworking is incomplete. The area of complete underworking is determined by means of angles of total displacement, i. e. the interior angles relative to the worked-out space, which are formed in the vertical main sections of a displacement trough by the seam lines and the lines connecting the boundaries of the worked-out space with the boundaries of the flat bottom of the trough. It is distinguished between the angles of complete underworking in sections across the strike: "' 1 at the dipping end and", 2 at the rising end of the worked-out space (Fig. 11.10) and those in sections on the strike; "' 3 at both sides of the worked-out space.

.1. ~I

0/1

\1

~I

Fig. 11.10 Complete underworking angles

278

Ch. 11. Rock

Disturbance

The process of rock displacement is often characterized by the coefficient of underworking which is understood as the ratio of the length of a stope working to the minimal length required for complete underworking of the Earth's surface in the given direction. The coefficients of underworking can be determined along the dipping line and on the strike of a seam. Denoting, respectively, the actual dimensions of a working on the dip and on the strike by Dl and D2 and the minimal dimensions for complete underworking by DOl and Do2, the coefficient of underworking on the dip will be nl = Dl/Dol and that on the strike, n2 = D2/Do2. An important characteristic of underworking is the ratio of the length of a longwall D to the depth of a mine H at which complete underworking occurs. It is taken that complete underworking takes place at nl :;:?;1 and n2:;:?;I. In many cases, rock displacement causes fissures in the trough. The portion of the displacement trough in which fissures are observed is delineated by rupture angles (caving angles), i. e. the exterior angles relative to the worked-out space, that are formed in the vertical main sections of the displacement trough by a horizontal line and the lines connecting the boundaries of the worked-out space with the nearest surface fissures at the trough edges (Fig.ll.ll). It is distinguished between the rupture angles in sections across

Fig. 11.11 Rupture angles

and Protection

of Structures

(a)

1 Ib)

\=::7 A

AI jc)

A

"\\

8

82

~

' \ \

--~C 81

8 \

c

~~

"

A

81 Fig. 11.12 Deformations: (c) r~spectively compressive deformations

(a) vertical; (b) and and tensile horizontal

the strike (13"and y") and those in sections on the strike (0"). Surface subsidence (11), i. e. the vertical component of the displacement vector, has been studied much more thoroughly than other parameters. It is distinguished between the maximum subsidence in complete underworking, 110' and that in incomplete underworking, 11m. Vertical deformations may arise due to non-uniform subsidence and are characterized by inclination, curvature, and radius of curvature. Referring to Fig. 11.12a, points I, 2, 3 are bench marks on the surface before under-

11.3.

Rock

Displacement

working and J', 2', 3' are the same points after underworking; 111'112'113are the subsidencesof respective bench marks; 11-2' 12-3 are the distances between the points before underworking; and ~1' ~2' ~3 are the horizontal displacements of respective bench marks. The inclination of an interval on the surface is determined relative to the initial position of that interval. For instance, the inclination of a section 2-3 after underworking is expressed by an angle i2-3. In practice, inclination is measured as the difference of subsidences of extreme points of a section related to the initial length of the section: '2-3 = 113-112 4-3 The inclinations of adjacent sections in a displacement trough are in most cases different. This non-uniform subsidence gives rise to another kind of vertical deformation, curvature. Non-uniform subsidence of the surface can be characterized by the difference of inclination angles of two adjacent sections: k2 = i2-3 -il-2 11-2/2 + 12-3/2 i. e. curvature is the ratio of the difference of inclinations of two adjacent sections to the half-sum of the lengths of these sections. The radius of curvature is the inverse of curvature: R = l/k Horizontal deformation is one of the most important characteristics of surface subsidence. Let us analyse the combined motion of two surface points, A and B (Fig. ll.12b). As a result of displacement, the point A will be shifted to A1 and the point B, to B1. In the case of the compression of a section AB, vectors AA 1 and BB 1 will be directed as in Fig. 11.12b and in the case of tension, as in Fig. 11.12c. Let a line parallel and equal to the vector

279

Parameters

AA 1 be drawn through the point B. It is also clear that AlBl is the length of the section AB after surface deformation. The relative horizontal deformation will be: E --AB-AB

AB-

AlBl

CB2 -AB

Thus, horizontal deformation (tensile or compressive) is the elongation or contraction of the initial length of a section related to this length. The duration of the displacement process may be of interest mainly when deciding on the possibilities of the construction of buildings on an underworked area. It is agreed to distinguish three stages of surface subsidence: the initial, active, and attenuating. The initial stage, i. e. that during which deformation initiates, usually continues to the moment when a mine is advanced under a particular observation point and can be characterized by the subsidence rate from tenths of a millimetre to 1-1.5 mm per day. The active stage is the period in which the rate of subsidence exceeds 50 mm/month on gently dipping seams or 30 mm/month on steep ones. The displacement process is considered to be finished at that day of observations after which the total subsidence during six months does not exceed 30 mm. The duration of the subsidence process mainly depends on the depth of the mining work, thickness of seams, and the physicomechanical properties of rocks. The path of the motion of surface points and the distribution of displacements and deformations within a displacement trough obey definite regularities. As a mine face approaches, the paths of points deviate from the vertical towards the face. After the face has ed beneath the points, their paths deviate towards the advancing face. Finally, as the face has been moved sufficiently far, the paths of points become perfectly vertical. When solving problems associatedwith the protection of surface structures, it is essential

280

Ch. 11. Rock Disturbance

and Protection

~

Fig. 11.13 Distribution of surface displacements and deformations: 1-vertical displacements; 2horizontal displacements; 3- horizontal deformations

to know the distribution of displacements and deformations within a displacement trough. It is usually sufficient to analyse the distribution of the following elements in a trough: the maximum values of the horizontal and vertical components of motion; maximum deformations in the main sections of the trough on and across the strike; maximum inclination; maximum curvature; and maxifuum elongation and contraction. The curves of the distribution of surface deformations on a gently dipping seam in a section across the strike are illustrated in Fig. 11.13a. With horizontal and gently dipping seams, the curves of inclinations usually follow the pattern of the curves of horizontal displacements. The curves of curvature are similar to the curves of horizontal deformations. With horizontal (flat) seams, the points of essential importance, in addition to boundary points A and B, are also points E, £1, and 0.

of Structures

The last point is the point of the maximum subsidence, minimum horizontal displacement, and maximum contraction. The points E and El are the inflection points of a subsidence curve. They are the points to which the maximum inclination, maximum displacement, and zero horizontal deformation are confined. The maximum tension is observed roughly amid between the inflection points and trough boundary. With an inclined bedding of seams (Fig. ll.13b), the patterns of these curves are different. With an increase in the angle of dip of seams,a curve 1 becomes more asymmetrical on the rise: the point of zero horizontal displacement does not coincide with the maximum subsidence point, whereas the points E and El become asymmetrical relative to O and O 1. The asymmetry of curves increases further with an increasing angle of dip of seams. 11.4.

Factors Responsible for Rock Displacement

Physico-mechanical properties of rocks and bedding conditions. The state of rocks is largely responsible for the pattern of displacement. For instance, with loose-grained rocks having a low cohesion, subsidence proceeds rapidly, appears sharply on the surface, and often leads to the formation of ledge-shaped fissures. A typical example is the Moscow district coal basin where, with the mining work carried out at a depth of 40-50 m, the roof subsidence becomes noticeable on the surface already in 2 or 3 hours. Plastic rocks, such as clay shales, promote plastic deformations, so that rock displacement occurs uniformly and smoothly following the advancement of a mine face; the surface subsides slowly and does not cause large damage to surface structures. The structure of a deposit can influence substantially the pattern of displacement. With alternating hard and soft rock strata in

11.4.

Factors

Responsible

a bed, secondary subsidence can appear in the mine roof, especially when quickly caving soft rocks lie immediately on the roof, whereas the layers (bands) of hard rock are overlying and hang up periodically over a large area. Poorly predictable cavings of these bands can develop an elevated rock pressure in stope workings and adjacent preparatory workings and sometimes are the cause of emergencies and rock bursts in mmes. Quicksands can complicate substantially the process of rock displacement. Cases have been recorded when quicksands occurring in the rock massif being underworked caused sharp flattening of displacement angles. Underworking of quicksands can involve large water losses, which can result in surface subsidence far ahead of the working face. The angle of dip of a deposit is among the critical factors governing the rock displacement process qualitatively and quantitatively. The pattern of displacement of the overlying rock is closely associated with the angle of dip. With steep angles of dip, substantial shear deformations in displaced rock are quite typical. With horizontal or gently dipping seams, the main kind of deformation is bending of rock strata. With steep bedding, the horizontal component of a displacement vector is predominant, whereas the vertical component prevails in the rock displacement on flat seams. It is found by observations that, under similar conditions, structures above workings in seams with steeper angles of dip suffer from greater deformations. For instance, in the Donetsk coal basin, mining in gently dipping seams at a depth of 200-250 m causes no fissuring on the surface, whereas the mining work in steep seams, even at a depth of 600 m, can lead to the appearance of large rupture cracks on the surface. An increase in the angle of dip of a deposit involves a change in the position of a displacement trough relative to the worked-out space, i. e. the trough is shifted towards the

for Rock

Displacement

281

strike. The distribution of hazardous zones in a trough is also associated with the angle of dip. A steeply dipping structure of a deposit, sharp changes in the angle of dip, folded bedding, and the presence of moderate and large tectonic disturbances can lead to the appearance of concentrated deformations, fissures and ledges in the surface. Depending on the thickness of seams and bedding depth, these deformations may vary from a few millimetres to tens of centimetres and are quite dangerous for surface structures, since structures located on ledges then suffer from substantial deformations or even break down if these deformations exceed 20-30 cm. The sites for the construction of new objects should, as a rule, be located on non-underworked territories or on those with favourable geological conditions. If a need arises to erect new objects in underworked zones which can cause the appearance of large deformations and ledges, protective measures should be taken to increase the strength and spatial rigidity of buildings and structures (reinforced-concrete, belts in the underground portions of buildings, cast-insitu concrete foundations, reinforced ts, continuous horizontal reinforced-concrete belts at the level of floor ceilings and partitions, division of buildings into sections, provision of horizontal sliding ts, etc.). The construction of new objects on areas above old stope workings at depths of 20-80 m can only be started after preliminary geological examination to reveal empty cavities in the worked-out space. The construction of residential buildings above the zones of preparatory mining workings at depths less than 10 m (where m is the height of a working) is possible only after geological examination for determining the non-caved portions of workings (voids). In all cases, detected voids should be filled in. The depth of the mining work can influence substantially the magnitude of rock displa-

282

Ch. 11. Rock

Disturbance

and Protection

of Structures

cement and the time and rate of its ma- cohesion), which in turn leads to a loss of nifestation. With an increase in the mining stability of slopes and landslide phenomena. The disturbance of the rock massif by old depth, the amount of displacement decreases and the process becomes smoother and less stope workings. Numerous field observations dangerous for surface structures, though this have demonstrated that the mining work in a is true only to a certain depth. An increase in disturbed rock massif can activate rock disthe depth of the mining work always in- placement by increasing deformations, rates, creases the time of the displacement process. and non-uniformity of surface subsidence. The thickness of an extracted seam. Com- The activization of rock displacement may be pared with the depth of the mining work, the due to the following factors: (I) voids formed due to hanging up of thickness of a seam has an inverse effect on overlying rock layers during primary unthe rock displacement: with a larger thickness, the process of displacement is more derworking. Repeated underworking can largely eliminate hang-ups and produce better pronounced and involves higher horizontal and vertical deformations. With an appre- compaction of the disturbed rock massif; (2) primary underworking decreases the ciable thickness of a seam, the zone of smooth sagging can disappear fully, and the strength of a rock massif by opening old and rock then subsides by caving and with the forming new fissures. For that reason, rock displacement on repeated underworking proformation of terraces. On seams of a small thickness, the rock ceedsat a high rate, since it takes place in the displacement occurs mostly by bending of rock massif with impaired strength properstrata. The cave-in zone develops only weak- ties. ly and only in the direct vicinity of the Working systems.The principal parameters of working systems which can influence rock worked-out space. The presence and thickness of sedimentary displacement are the height of levels, length rocks and the surface relief In bed rocks, the of a mining field, method of roof control, rate .rock displacement occurs so that points , of face advance, and the completeness of move almost along the normals to the bedding mineral extraction. The height of a mining level and the length plane. In sedimentary rocks of an appreciable capacity, the rock displacement occurs in of a mining field are equally important, since directions from the edges to the centre of a they determine the shape of a displacement displacement trough. In the s on the trough. With small dimensions of the workrise of a seam, sedimentary rocks and bed ed-out space, a cup-shaped trough usually rocKs are displaced in opposite directions, forms. With an increase in the space di. which often causes the separation of sedi- mensions, a cup-shaped trough changes to a mentary layers from the bed rock and the plate-like form. The best method of roof control to prevent destruction of underground objects. The effect of the surface relief on rock the surface subsidence is backfilling of the displacement is appreciable only in moun- worked-out space. The filling decreases the tainous regions where underworking of steep size of voids, s the overlying rock, and slopes often triggers landslides. Rock stability decelerates and decreasesto a certain extent depends substantially on the angle of internal the process of rock displacement. The effect of filling depends on the filling friction and the cohesion at slip planes. The rock displacement then results in loosening of material used. Continuous dry filling decreasthe rock massif and associated reduction of es the volume of voids only insufficiently the strength properties of rock (mainly of (sometimes only by 40 per cent). Hydraulic

11.5. Monitoring

Rock Displacement. Observation Stations

filling and hardening filling produce the most favourable effect on surface subsidence. With carefully packed hardening filling, the surface subsidence may be as low as only 3 per cent of the seam thickness. In this case, surface displacements are uniform and smooth, so that even large structures settle down slowly and without large damage. With continuous working systems, especially with a large-Iength longwall and complete roof caving, surface displacement occurs smoothly and uniformly. With pillar and room-pillar working systems having roof caving where safety pillars are left at short intervals in the worked-out space,the overlying rock massif may be broken by the pillars into individual blocks, with fissures propagating up to the surface and causing largely uneven subsidence. 11.5.

Monitoring Rock Displacement. Observation Stations

An observation station on the surface is a system of fixed points (bench marks) placed in the ground or surface structures (Fig. 11.14). Bench marks are usually set up along the profile lines on and across the strike of a deposit. In mountainous, wooded and densely built-up areas, broken profile lines are permissible. When examining the underworking conditions for railroads, pipelines and other stretched objects, the profile lines may be arranged diagonally to the strike. In some cases, say, for monitoring underground gas pipelines, stations may be established as a network. An observation station is set up according to the design plan which includes an explanatory note and graphical appendices. The graphical material of the design plan should contain: (a) a t plan of the land surface and underground workings with profile lines of an observation station (on a scale

283

1/500, 1/1000 or 1/2000); it should give the boundaries of the mining field, the current state of the mining work and its further development, the supposed position of the displacement zone, tectonic disturbances, and the scheme of junction of control points; (b) geological cross sections along the profile lines with indication of the workings; and (c) the designs of control and working bench marks. The place for establishing the observation station is chosen by considering the positions of mining workings and according to the particular object of observations. An area on a flat country with few structures and away from haulage tracks and roads is a convenient place for an observation station. Usually, two profile lines across the strike and one on the strike are laid out. When working deposits with varying geological and mining conditions, the profile lines are laid out separately on the sections which differ from one another in the bedding elements, thickness of a seam, working system, etc. The profile line across the strike which is the closest to undisturbed (intact) rock is located at a distance not less than 0.85 Hm from a breakthrough or the point where the face is stopped (Hm is the mean depth of a working). If the longwall face has already moved from the breakthrough, the distance from the latter to the profile line is found by the formula: d = Hm cotalloo :;::?; 0.85Hm The next profile line is laid out at a distance of 50 m from the previous one. The length of profile lines drawn across the strike (Fig. ll.l5a) is determined on vertical sections by the boundary displacement angles. Two control bench marks are established on the continuations of the profile lines beyond the expected displacement zone. The distance from the first control bench mark to the end of the working portion of the profile line should be not less than 50 m, and

Ch. 11. Rock

Disturbance

and Protection

the spacing between the control bench marks, 50-100 m depending on local conditions. The profile line on the strike es through the point of the maximum subsidence of a displacement trough. To find this point on the vertical section across the strike, a line is drawn at an angle 9 from the middle of the worked-out space up to its intersection with the surface. The length of the profile line on the strike is found in the following way (Fig. ll.15b). The point where the face will be supposedly stopped is projected onto the surface (point k). A distance B = Hmcotan 00 is the~ laid off

of Structures

towards the undisturbed rock massif, and a distance 1.75Hm, towards the worked-out space. Control bench marks are established by the same rules as for the profile lines across the strike. Working bench marks are set up along the profile lines at intervals decided by the depth of the mining work. Bench marks should be designed so as to ensure their stability and preservation for a long period; in addition, they should be inexpensive and convenient for establishing and observations. Bench marks for long-term

11.5.

Monitoring

Rock

Displacement.

Observation

Stations

285

(b)

Fig. 11.15 strike

Determination

of length of profile

lines: (a) in section across the strike; (b) in section on the

and ordinary stations are made from metal tube sections, studs or rail pieces which are set up below the freezing line and concreted. For temporary stations, they can be made from wooden stakes or pegs driven into the soil. For better preservation, bench marks are often buried in the ground to a depth of 30-40 cm. Observations. Observations at stations on the surface include tying (connecting) control bench marks to an existing reference net, primary observations on the bench marks in horizontal and vertical planes, and secondary observations. The horizontal connection of control bench marks is carried out by triangulation or by closed theodolite traverses. It is permissible to run a hanging theodolite traverse, provided that the angles and sides are measured in the forward and back direction. The permissible relative discrepancy of a theodolite traverse should not exceed 1/2000. The vertical connection of control bench marks is done from the points and bench marks of a levelling net by means of geometric levelling with a discrepancy not more than

15 JL, mm (where L is the length of a level line, m). Upon connecting a station, it is possible to start primary and secondary observations. A complete set of instrumental observations contains: the levelling of all bench marks; the measurements of bench spacings along profile lines; determination of the deviations of working bench marks from a profile line; surveys of surface fissures with records of the time of their appearance; and the measurements of the deformations of structures. The first observation at a station is recommended to be carried out in 7-10 days after setting up of bench marks (if these have been concreted) or in 2-3 days for bench marks driven into the ground. Primary observations are carried out twice, and the final result is obtained as the arithmetic mean of the two observations. The time intervals between the observations depend on their task. If it is essential to obtain detailed information on rock displacement, at least four intermediate observations between the initial and final observa-

286

Ch. 11.

Rock

Disturbance

and Protection

tion should be made, in time intervals determined by the formula: t = H/6c where H is the depth of the mining work at the lower boundary of a working and c is the rate of the face advance, m/day. During the initial and active stage of rock displacement, observations are carried out at least three times a month and during the attenuation stage, at least once a month. After checking field measurements, the displacements and deformations are calculated, and curves are plotted. Calculations are made by the formulae: subsidence: 11= Hn -Hn-l (11.1) inclination: i = (11n-11n- J/I

(11.2)

curvature: k = (in -in- J/lm

(11.3)

horizontal displacement: ~ = D2 -Dl

(11.4)

and horizontal deformation: E=(ln-In-J/I

(11.5)

where 11is the subsidence of a bench mark; Hn- 1 is the absolute elevation of the bench mark in the previous observation; Hn is the absolute elevation of the bench mark in the current"observation; i is the inclination of a subsidence curve; k is the curvature of that curve; in and in -1 are the inclinations of the current and previous interval; ~ is the horizontal displacement; Dl, D2 are the distances from a control bench mark to the given bench mark in the previous and current observation; E is the horizontal deformation; In' In- 1 are the length of intervals in the current and previous observation; and Im is the half-sum of the lengths of intervals in the previous and current observation. The calculated deformations and displace-

... .. :E .~

of Structures

11.6.

Calculations

of Rock

ments of the Earth's surface are tabulated as given in Tables 11.1 and 11.2. 11.6.

Calculations of Rock Displacement

An increase in the depth of the mining work leads to an increase of the zones of harmful effects on the surface, and therefore, more objects on the surface will be subjected to these effects and require protection. On the other hand, with an increase in the mining depth, surface deformations decrease,so that it becomes possible to underwork even critical structures which could not be underworked when mining was done at higher mining levels. In densely inhabited areas with multistorey residential and public buildings and extended networks of gas and water supply and seweragesystems,underworking requires complicated engineering calculations for determining the expected deformations and degree of damage to structures. It is also needed to carry out observations on the surface subsidence and the state of structures and control the protective measures and the repairs of damilged buildings. The existing methods of calculation of rock subsidence can be divided into the following groups: (a) empirical methods; (b) methods based on distribution function; and (c) methods based on theoretical models. Empirical methods are the most preferable since they use the results of direct observations on subsidence. Among the empirical methods, the method developed in this country is quite accurate. It is used in cases when the roof control is effectedby complete caving of the back-filling of the worked-out space and is applicable when the underworking ratio is Him > 20 for the angles of dip between 0° and 55° or Him > 15 for the angles larger than 55°. The underworking ratio is here the ratio of the mean mining depth H to the extracted or effective thickness of a seam, m.

Displacement

287

Depending on the completeness of initial data, it is possible to detennine the expected or probable displacements and defonnations of the Earth's surface. The expected displacements and defonnations can be calculated when the calendar plans of the mining work development are available and the probable ones, when there are no such plans. In the calculations of the expected displacements and defonnations of the Earth's surface, the following characteristics are detennined: subsidence 11,horizontal displacements ~, inclinations i, curvature k and curvature radius R, horizontal defonnations E, and displacements and defonnations caused by rock motion along the bedding. If the angle of dip a is smaller than the limiting value a" the expected displacements and defonnations are detennined by the calculation method for the conditions when there is no rock motion at the lying wall. If the angle of dip is equal to or greater than the limiting value, the calculation method considers rock motion at the lying wall. The limiting angle of dip of a seam, a" is the angle at displacements thewhich lying dangerous wall can appear. , of rock at The calculation of displacements and defonnations is started from constructing the geological sections on and across the strike, in which sedimentary and bed rocks should be indicated. These sections should also show the driven and projected workings (with the dates of driving), the depth of the mining work, and the dimensions of workings and pillars. The extracted thickness m of a seam is detennined as the total sum of the thicknesses of layers of coal and enclosing rock extracted from the stope workings. With back-filling of the worked-out space, the calculation of displacements and defonnations is carried out by considering the effective thickness of the seam: mer=(hc+hin)(I-BJ+Blm (11.6) where hc is the convergence of the roof and

Ch. 11. Rock

288

Disturbance

and Protection

of Structures

Table 11.2 Bench

mark

Interval

length,

m

No.

Subsidence Inclination Inclination Curvature difference of i difference k, l/m interval ends, mm

2 3 4 5 6 7 8 9 10

156.262 9.893 10.031 10.002 10.134 10.062 9.951 9.943 9.972 10.051

0 +1 O +1 +1 +2 +2 +2 +5 +1

Radius of Subsidence Inclination curvature difference of i R. m interval ends, mm O

°

+ 0.1 + 0.1 °

+ 0.1 + 0.1 + 0.2 + 0.2 + 0.2 + 0.5 + 0.1

floor before back-filling (if there are no observation data and the face is advanced by 8-20 m ahead of the filling, hc is taken equal to 0.15 m); hin is the incompleteness of filling (mean distance from the top of a filling massif to the roof of a seam), which is determined experimentally; m is the extracted thickness of a seam; and B 1 is the shrinkage factor of filling whose values are given below: Hydraulic filling: B1 sand. 0.05-0.15 crushed rock. .0.15-0.30 Pneumaticfilling 0.25-0.40 Gravity-f1owfilling: crushed rock. .0.25-0.45 ordinary rock. .0.35-0.50 In the calculations of displacements and deformations, it is essential to consider the influence of all projected stope workings and of those driven earlier, which can activate the displacement process in the given section. The maximum subsidence of the Earth's surface is found by the formula: llm = qomcosaNllN2 (11.7)

0.03 -0.01 +0.01 0.00 +0.01 0.00 0.00 +0.03 -0.04

+0.1 -0.1 +0.1 0.0 +0.1 0.0 0.0 +0.3 -0.4

0

+33.3 -100 +100

+100

+33.3 -25.0

+3 +4 +8 +8 +4 +23 +45 +73 +136

+ 0.3 + 0.4 + 0.8 + 0.8 + 0.4 + 2.3 + 4.5 + 0.73 +1 3.5

where qo is the relative maximum subsidence; m is the extracted thickness of a seam; a is the angle of dip of a seam; and N 1 and N 2 are the factors depending on the ratio of the design length of a longwall Dd to the mean mining depth H, T he subsidenceof the Earth's surface in the pdints of the main sections of a displacement trough is determined by the formula: Tl(x,y) = TlmS(z) (11,8) where S(Z)is the function of a typical subsidence curve, which depends on coefficient N 1 and N 2' The inclinations in the main sections of a displacement trough are determined by the following formulae: for a half-trough on the strike: F(

~

1 zx,

L3 for

a half-trough

on the dip:

11.6.

Calculations

of Rock

289

Displacement

lst-4th observations Inclination difference

Curvature k. Radius of curSubsidence I/m vature R. difference of m interval ends, mm 0

+0.3 +0.1 +0.4 0.0 -0.4 +1.9 +2.1 +2.8 +5.2

+0.01 +0.01 +0.04 0.0 -0.04 +0.19 +0.21 +0.28 +0.52

Inclination i

+25.0 -25.0 +52.5 +47.5 +35.7 +19.2

+6 +9 +10 +9 +13 +27 +57 +79 +163

Curvature k, I/m

+0.6 +0.3 +0.1 -0.1 +0.4 +1.5 +2.6 +2.5 +3.5

+0.02 +0.03 +0.01 -0.01 +0.04 +0.15 +0.28 +9.25 +0.85

Radius curvature m

of R,

0

+ 100.0 + 100.0

Inclination difference

+0.6 +0.9 +1.0 +0.9 +1.3 +2.8 +5.4 +7.9 +16.4

+I -I + + + + +

50.0 33.3 00.0 00.0 25.0 67.5 38.5 40.0 11.8

T he horizontal displacements of the points in the main sections of a displacement trough are found as follows: for a half-trough on the strike: fox = O.5ao1lmF'(zx) for a half-trough

(11.15) on the dip:

f,yl = O.5aoTlmF'(zyJ

and for a half-trough ~y2 = O.5aoTlmF'(Zy2)

(11.16) on the rise:

(11.17)

where the factor ao is the relative maximum horizontal displacement and functions F'(zx), F'(zyJ, and F'(zyJ are the same as in formulae (11.12)-(11.14). The horizontal deformations (tensile and compressive) in the main sections of a displacement trough are determined by the formulae: for a half-trough on the strike:

"x = O.5ao -L1lmF'(zx) 3 19-1270

(11.18)

290 for a half-trough

Ch.1

Rock

Disturbance

on the dip:

Eyl = O.5ao ~ F'(zyJ Ll and for a half-trough

E = 0.5a ~ F'(z ) y2 O L2 y2

on the rise

of Structures

of surface structures will be discussed below. I. Mining measures may consist in (a) the (11.19) protection of structures by back-filling of the worked-out space and (b) the application of special methods of mineral extraction, which ensure proper safety of surface structures. (11.20) Among these methods, it is worth to mention the following: (a) extraction sections are plan-

where functions F'(zx), F'(Zyl)' and F'(Zy2) are the same as in formulae (11.12)-(11.17). 11.7. sMe;sure;t ur ace

and Protection

for tProtectIng .quickly ruc ures

ned so that the surface structures turn out to be on the portions of a displacement trough where earth subsidence is the most uniform; (b) a stope face is advanced continuously and as toworking minimizeonthe time structures; of influence of theso stope surface and (c) mineral is extracted at both sides of a

The problems of the protection of buil- breakthrough which is located under the dings and structures against harmful effects centre of a surface structure, etc. of underground mining have become crucial One of the most efficient methods of in recent time, especially in large coal fields structure protection is the provision of strip where underworking of buildings leads either pillars having a large strength margin and to a substantial increase of the cost of mining spaced at intervals which ensure proper sta(owing to expensive additional measures for bility of the roof. The essenceof the method the protection of buildings) or to large losses consists in the following: ~s the intermediate of coal in safety pillars. chamber pillars, which are left between the The conditions of safe mining are determi- barrier pillars, are destroyed, the caving proned by using the concepts of permissible cessis localized in the space confined between deformations and ultimate deformations. the. barrier pillars. In that case, the overlying Permissible deformations are taken as the rock will cave in only within the equilibrium deformations of the Earth's surface which dome, whereas the rock massif above it cause only repairable damage to surface remains undisturbed. structure. Ultimate deformations of the Earth's 2. Construction measuresdecreasethe stressurface are understood as the ultimate limit ses and deformations in structures and builfor deformations; any deformations above dings and increase the load-carrying capacity, this limit"Will be dangerous for the stability of but do not exclude the appearance of fine buildings and structures and the life of people. fissures in walls, foundations, and floors. The For determining the conditions of safe principal construction measures for minimiunderworking of objects above a single seam zing the deformations of structure are as or the first seam of a suite, it has been follows: proposed to use the concept of safe mining (a) settlement ts by which long buildepth which is understood as the depth dings are divided into sections of a suitable below which mining operations cannot cause size and closed contour. Settlement ts are in structures the deformations exceeding the arranged near internal partition walls. Their permissible ones. At mining levels below the thickness should be such that the building safe depth, the mining work can be carried sections can settle down independently under out without taking protective measures. the effect of underworking. It is recommenThe principal measures for the protection ded to divide a building by settlement ts

11.8.

Construction

to its entire height (except for the foundation); (b) yieldable foundations which absorb the horizontal stressesin buildings. This is achieved by providing a horizontal t to separate the underground portion of a building from the foundation; the t is filled with a material having a low coefficient of friction; (c) foundation plates. The idea consists in that a reinforced-concrete plate is laid onto the levelled and compacted soil surface. The plate is cut through by diagonal ts filled with an elastic material. A layer of wet sand up to 5 cm thick is laid on the plate and above it another plate (without ts) is placed on which the building will be erected. Effective protection of buildings against the effect of underworking is provided by compensating ditches dug in the ground along a building; they diminish horizontal deformations by 33-50 per cent. The bottom of a ditch is made somewhat lower (around 50 cm) than the foundation foot. Compensation ditches are filled with corrugated steel, fine coke or a mixture of soil and sawdust. 3. Safety (protective) pillars are left in the worked-out area of mines. This method is resorted to when other protective measures are inefficient or too expensive.

11 .8.

Construction of Safety

Pillars

Safety pillars can be constructed by the method of vertical sections or method of perpendiculars.

11.8.1.

Method

of Vertical

Sections

Let us consider two examples of the application of this method: construction of safety pillars for a building and for an extended object. Example 1. It is required to construct a safety pillar for a four-storey brickwork 19.

of

Safety

Pillars

291

building of a rectangular form 28 x 45 m in plan (Fig. 11.16) and arranged diagonally (at 45°) to the strike of a seam. Another seam, 11, of a thickness m = 0.9 m and an angle of dip a = 30°, lies under the seam mentioned. The thickness of sedimentary rock is 25 m. The displacement angles are:

292

Ch. 11. Rock

Disturbance

and Protection

of Structures

2004080m I I I I I I I

a Fig. 11.16 Construction of safety pillar for building by method of vertical sections

tions of the pillar, the plan contours of the the bed rock on the dip. The two latter angles can be found from the formulae: pillar are determined (abcd). The reserve of coal in the pillar is calcula- cotanf3' = Jcotan2f3 cos2e + cotan2o sin2e ted by multiplying the seam thickness by the cotany' = Jcotan2y cos2e + cotan2o sin2e total area of the pillar. Example 2. It is required to construct a safety pillar for a railway bed in a brown coal where 13,y, and O are the displacement angles field (Fig. 11.17).The railway bed is arranged in the main sections of a displacement trough diagonally to the seam strike. The seam for the given seam and e is the acute angle thickness is 1.3 m and the angle of dip, 25°. between the strike line of the seam and the The overlying bed rock is represented by clay contour of the object to be protected. The boundaries of the safety pillar are shales, argillites, and aleurolites. The thickness of sediments is 20 m. The displacement determined by plotting a number of vertical angles are: ~ = 47°, y = 65°, O = 65°, and sections perpendicular to the railway line in

~

11.8.

Construction

of Safety

Pillars

293 7-8

9-10 10

/ --8

?

400 -375 -~

--

~o

9

~

47~

/ ~o--

~5° 5-6

~

45O

-I

0°

---

3-4

4

° 5

,

--~~~.6

4

50 I I

45°

~6O I

-45°

-,-I

I,

65°I I

I

350 --

1-2

2

325 -

45° -45" .rI

300

W

225

3

/

~~

!1 SectionNo.1 6113'11'1 1-2 '~1561651

3-4

Fig. 11.17 Construction of safety pillar for extended object by method of vertical sections

rock at displacement angles J3iand yi. The bedding deptb of the seam under the railway bed is determined as the difference of elevations between the Earth's surface and the seam foot. This depth is laid off in the sections, and the line of the seam is drawn at an angle ai through the points thus obtained.

The angle of dip of the seam ,in the section plane is determined graphically. The points obtained by the intersection of seam traces with protection planes are transferred onto the plan where straight lines or smooth curves are drawn to determine the contours of the pillar. Seam outcropto overburden

<)6

278~ 200 -

/

" ,---

2 "~--~'2'

280~ 150-

" .',

1~

250~

-""

100

Fig. 11.18 Construction of safety pillar by method of perpendiculars

Ch. 11. Rock

11.8.2.

Method

Disturbance

of Perpendiculars

In this method, the boundaries of a pillar are obtained directly on a plan, i. e. without plotting vertical sections. The lengths of perpendiculars are determined by the formulae: (H -M) q=

1 + cotan [3' tan 11cos e (H -M)

I=

cotan [3'

1 -cotan

cotan y' y' tan 11cos e

where q is the length of perpendiculars to the rise; I is the length of perpendiculars to the dip; H is the depth from the Earth's surface to

and Protection

of Structures

the seam foot; a is the angle of dip "of the seam; M is the thickness of the sedimentary rock; and 13' and y' are the displacement angles. Consider, as an example, the construction of a safety pillar for a railway bed ing diagonally to the strike (Fig. 11.18). Points are chosen in the characteristic places of the protected area and perpendiculars are drawn in these points to the contour of a safety berm. The corresponding lengths q and 1 are laid off along the perpendiculars. Points 1, 2, 3, J', 2', and 3' are connected by lines which define the boundaries of the safety pillar. The coal reserve in the pillar is then calculated.

Chapter

Stability

12.1 Principal

Twelve

of Quarry

Flanks

in quarry flanks can be divided into five principal kinds: taluses, downfalls, landslides, subsidences, and mud-streams {mud-flows). Rock displacements in open-cast mining of A talus takes place when small volumes of minerals determine to a large extent the loose rock roll gradually from the top of a mining economics and labour safety. slope to its bottom. This can occur when the The loss of stability (displacement) of angle of a slope is steeper than the angle of flanks and benches in quarries is mainly internal friction of loose rock, and the latter associated with changes in the stressed state has practically no internal cohesion. of the undisturbed rock massif, which can be A downfall is essentially quick movement caused by open-cast mining. of rock masses along slip surfaces, such as In this process, the destruction of rock surfaces weakened by geological disturbances mainly occurs under the action of tangential or fissures. These surfaces may be plane or stresses which under particular conditions curved, in the latter case, mostly circular-cycan induce irreversible shear deformations in lindrical. the rock massif along the surfaces called slip In order to prevent downfalls, .quarry flanks and benches are designed by consideplanes. The studies of the patterns of stressed state ring the specific characteristics of the rock in quarry flanks demonstrate that in the massif or by providing artificial measures for general case the distribution of shear stresses increasing the rock stability. in a rock massif weakened by a side cut (such Landslides are characterized by that the as a flank) may be represented by stress motion of rocks occurs slowly, the process diagrams like those shown in Fig. 12.1 (lines may continue for a long time and entrains 1-1, 11-11, and 111-111).The points of the large massesof rock. The moving rock massif maximum shear stresses,which are located at in a landslide is subjected to plastic deformadifferent heights of the flank, form the directions. Both bed rocks and rocks of waste tion of the weakest plane abcde.In the case of dumps may be involved into the process. ultimate stresses, this plane becomes a slip A subsidenceis essentially a vertical sinking plane. A slip plane of this kind mainly of loose rock masses at the edges of flanks, corresponds to a homogeneous (isotropic) which occurs without forming a continuous rock massif. If the massif has anisotropic slip surface. Landslides can occur on compalanes (bedding planes, ting systems, tion of loose rocks in waste dumps, which are tectonic disturbances, etc.), the position of a strengthened on wetting; on saturation of slip plane changes and in some casesmay be high-porous sediments with water; or in cases coincident with the planes of anisotropy. when there are soft plastic layers in the base The whole diversity of rock deformations of waste dumps.

Causes and Kinds of Rock Deformation

296

Ch. 12. Stability

Mud-streams (mud-flows) can occur in some rocks whose state changes from solid to fluid on water saturation. Mud-streams are observed most often upon saturation of loose and high-porous sedimentary rocks (loesses, loess-like loams, etc.) or when sands are carried off from sediments by filtering water flows. Mud-streams can be prevented by drainage. 12.2.

Factors Affecting Flank Stability

The stability of quarry flanks depends on the correlation between the forces that tend to retain a slope and those which displace it. These forGes can be influenced by many factors. The determination of the stable angles of inclination of quarry flanks (slopes) is essentially a problem of the theory of ultimate equilibrium according to which the strength of a rock can be characterized by a certain curve plotted in coordinates t, O"n(shear and normal stress),see Fig. l2.2a. A curve ARC in the figure determines the ultimate state of the rock in a specimen. A section OB' cut off by the curve on the t axis determines the cohesion. The angle of inclination of a

of Ouarry

Flanks

straight section mn to the an axis is called the angle of internal friction and the tangent of that angle is the coefficient of internal friction. A section OA describes the ultimate tensile strength of the rock, at' and a section OD is numerically equal to the ultimate compressive strength ac. In the general form the equation of the curve of ultimate equilibrium is 't = f(an) and can be described by a parabola, cycloid or a straight line depending on the kind of rock. A linear equation of equilibrium (Fig. 12.2b)has the form: 't = an tanp + k (12.1) where 't is the tangential stress in a shear plane, MPa; an is the normal stress in that plane, MPa; p is the angle of internal friction of the rock, degrees;and k is the coefficient of cohesion of the rock, MPa. The curves of ultimate equilibrium are plotted by the results of shear tests of rock specimens. A real rock is essentially a complex medium possessing a certain non-uniformity (anisotropy) of properties. The main factor responsible for anisotropy is the structure of a rock massif, in particular, various planes of weakness (bedding and stratification planes, fissures, etc.). Because of anisotropy, the laws

12.2. Factors Affecting

Flank Stability

297

Fig. 12.2 Strength certificate: (a) with curvilinear envelope of Mohr's circles; (b) with straight envelope

of geometrical similarity which are true for isotropic solids (metals, plastics, etc.) are inapplicable to rock massifs. For that reason, the mechanical properties of a rock massif may differ from those obtained by testing rock specimens. The properties of rocks in a massif are determined by special tests of rock prisms delineated in their natural bedding and oriented in a definite way relative to the planes of anisotropy. Forces p applied to a prism are developed by ,powerful jacks (Fig. 12.3). A prism usually breaks along a certain surface ab. The knowledge of the position of this plane makes it possible to determine the strength characteristics of a rock massif. Experiments have shown that among the two parameters characterizing the shear strength (cohesion and angle of internal friction), cohesion is subject to larger variations. Therefore, taking a particular value of friction by the results of laboratory tests of rock specimens, it is possible to determine the cohesion in the rock massif by considering that the resultant force of external pressure p can be resolved into a normal component N and a tangential component 1: If slip surfaces do not coincide with the planes of between rock layers in a massif, the angle of internal friction can be taken equal to the angle determined in shear

tests of rock specimens. The angles of internal friction for selected rocks are given in Table 12.1. The angles of internal friction at s of layers are taken equal to the angle of friction obtained by the results of laboratory tests for friction on these surfaces.The angles of friction obtained in tests at s of layers and fissures are given in Table 12.2. The mechanical properties of rocks in a massif (especially cohesion) not only differ from those in specimens,but are variable and depend substantially on the size ratio of the object being deformed, dimensions of structural blocks, and the strength of rock in specImens. During their formation and especially after the formation, rock massifs were subjected to

T

Fig.

12.3

Diagram

of natural

shear tests of priSJ

298

Ch. 12. Stability

Table 12.1 Rock

Sandstones Aleurolites Argillites Limestones Metamorphic schists Quartz-porphyries and granodiorite porphyries Syenites and porphyries

Angle of inter- Angle of renal friction in pose, degrees lumps, degrees 36 33 27-30 34 29

34-36 34-36 34-36 33-35 33-35

36

33-35

35

35

various changes and transformations which were associated with the appearance of rupture cracks, cleavages, stratification planes, etc. These surfaces divide rock massifs into individual polyhedrons or structural blocks which are essentially the elementary structural particles from which a rock massif is composed. In deformations of large rock massifs, structural blocks can be likened to mineral grains in small specimens subjected to deformations. Thus, for the estimation of the strength properties of rock massifs, it is essential to

of Quarry

Flanks

proceed from considering individual structural blocks. Plastic deformations of rocks are characterized by the appearance of two conjugate systems of fissures which, in the case of an isotropic medium, make an angle

Table 12.2

Porphyries, hornfelses, jaspilites, strong sandstones

28-31

Secondary quartzites, granodiorites, quartz-porphyries, granodiorite porphyries, skarnated rocks, syenites, diorites, aleurolites

25-28

Limestones, metamorphic schists, magnetites

24-27

Clay shales, argillites

23-26

Phyllites, talcochlorite and sericitic schists

23-25

24-28

22-27

20-26

20-23

17-20

23-25

20-22

16-19

21-23

18-20

15-18

20-22

13-15

9-12

12.2.

Table 12.3 (after

Factors

Affecting

Flank

299

Stability

G. Fisenko)

Rock group

Rocks and type of ting

Cohesion in lumps, MPa

III

Weakly compacted and weakly fissured sand-clay sediments; strongly weathered, fully kaolinized igneous rocks; compacted sand-clay sediments with normal ting

0.4-0.9

Strongly kaolinized igneous sand-clay rocks; compacted sandclay rocks with developed diagonal ting; moderatestrength laminated rocks mostly with normal ting Hard rocks mostly with normal ting Hard igneous rocks with developed diagonal ting

following fornlula suggested by G. Fisenko:

3.0-8.0

Coefficient a

0.5

10,0-15.0 15.0-17.0 17.0-20.0

3 3 4 5

20.0-30.0 30.0 20.0

6 7 10

entire complex of rocks and all structural elements of a deposit is involved into examiksp k = ( 12.2 m 1 + a In(H//) ) nation. In rock massifs divided into blocks by geological disturbances, each block should have one or two measuring sections. where km and ksp are the coefficients of With a simple structure of a deposit or cohesion of the rock in a massif and a quarry field, measuring sections can be spaspecimen, MPa; a is coefficient which can be ced at distances of 150-200 m from one found in Table 12.3; and H/l is the ratio of another. In each measuring section, there are the flank height to the mean size of structural determined the bedding elements of all blocks delinea~ed by fissures. ting systems, elements of stratification and Thus, for estimating the mechanical pro- foliation, linear dimensions of individual fisperties of rocks in massifs, it is essential to sures, distances between the fissures in each know the specific features of their ting, in ting system, pattern of fissure surface, and particular, the primary and secondary system the shape and size of structural blocks. of ts Uoint sets), contribution of each The bedding elements of fissures are measystem to the total quantity of fissures, sured by an inclinatorium. The total number spatial angles between the systems of ts, of measurements of bedding elements on an intensity of ting, patterns of distribution area depends on the number of ting of fissures in the quarry field, and the signifi- systems and the pattern of surface of fissures. cance of each ting system in the structure As a general rule, 15-20 measurements of of a deposit and the stability of slopes. bedding elements should be made for each The field observations of ting are car- ting system. With a large discrepancy ried out on natural and artificial rock out- between the measured results, the number of crops and in exploring and drainage wor- measurements should be increased up to 30. kings. The density of sections for the measOffice work consists in determining the urements of ting and their mutual ar- typical orientations of fissures and the intenrangement are deternlined by the geological sity {density) of ting. The elements of structure of a deposit or quarry field. Mea- fissure orientation in space can be measured suring sections should be located so that the most conveniently by means of stereographic

300

Ch. 12. Stability

grids. Statistical processing of stereographic grids makes it possible to divide the entire totality of fissures in the rock massif into particular systems. The number of fissures, i. e. the density of ting, can be determined by two methods: I. ~sually. i .e. by recording all detected fissures in each system; the results are then corrected by the data of statistical processing of a small number of selective measurements in systems. 2. By statistical processing of a fairly large number of measurements of bedding elements of fissures. The density of ting can be characterized by several coefficients: (I) a linear coefficient which gives the ratio of a unit length to the mean spacing between the fissures. In some cases, the unit length may be taken as the length of the object being studied, for instance, the height of a quarry flank, etc.; (2) an area coefficient. or the ratio of a unit area to the area confined between two pairs of fissures forming a structural block; and (3) a volume coefficient, i. e. the ratio of a unit volume to the volume of an averaged block. An important factor affecting rock stability is weathering, i. e. degradation of rocks on the Earth's surface caused by natural agents (temperature, water, oxygen, carbon dioxide, living organisms, etc.). Weathering effect is especially noticeable in the flanks of old quarries. Rock stability can be influenced substantially by hydrogeological factors: inflow of ground waters, hydrostatic and hydrodynamic pressure, suffosion, leaching, sudden water outbursts, and mud-flows. Acting separately or in combination, these factors can decrease substantially the strength characteristics of rock, in particular the shear strength. When estimating the stability of quarry flanks, it is also essential to take into consider-

of Quarry

Flanks

ation the climatic factors: atmospheric precipitation, local temperature conditions, microrelief, and wind velocity. Without proper drainage, atmospheric precipitation can cause the inundation of sand-clay rocks to a state when capillary water changes to gravitational water, thus reducing sharply the shear strength, and therefore, the stability of slopes. Temperature changes and winds often accelerate weathering and thus diminish rock stability. Some kinds of microrelief can be the cause of swamping. Rock stability can depend substantially on engineering factors, especially on the method of blasting work. After blasting, the strength of rock in some portions of the massif can drop to 20-25 per cent of the initial (natural) strength. In order to prevent landslides and downfalls, it is then required to change properly the elements of working systems (width of berms and platforms, heights and angles of slopes and benches, etc.), though sometimes at the expense of the mining productivity. It is also essential to consider other engineering factors which can influence the stability of, flanks, such as the width of stoping and transport berms, profile of working, platforms, underworking of flanks, etc. 12.3.

Mine-Surveying Observations on Rock Mining Deformations in Open-Cast Mining

Observations on rock disturbance in open-cast mining and processing of the results of observations are an important object of mine-surveying service in quarries. Observations on landslides include two stages: (a) exploration and detection of seats of landslides and (b) observations on landslide seats and development of particular measures to prevent landslide phenomena. In view of the continuous technological mobility of slopes in quarries, the organi-

12.3.

Mine-Surveying

zation of observations has certain specific features. Observation points established in slopes cannot be preserved for a long time (especially those on the benches of working flanks). In that connection, it is essential to organize observations so as to complete them in relatively short . There are two principal kinds of observations: (1) observations on visible deformations of flanks and benches in order to predict the shape of a landslide and the pattern of its development in space and time and (2) observations on sections where deformations are invisible but can appear and cause serious damage to the mining plant. The results of observations should establish the displacements of particular points of a rock massif in space and time; dimensions of a sliding massif, slip surfaces, stages of the displacement process (initial, active, and attenuating), and the degree of hazard of rock displacements for mining operations and for surface structures. For observations on rock displacements, observation stations are established on the flank of a quarry, and instrumental observations are made at them in specified time intervals. An observation station is essentially a system of bench marks set up along the lines perpendicular to the length of a quarry flank. In order to take into consideration the effects of various factors on flank stability, the profile lines of an observation station are usually located in sections of rocks having different geological conditions. The length of profile lines should be such that one or both ends of the line is beyond the zone of expected displacements. In quarries of a small depth, profile lines can be drawn through the entire quarry. Spacings between the bench marks of a profile line depend on the quarry depth and dimensions of benches.At least two bench marks should be established on each bench: one near the bench crest and the other at the foot of the overlying bench. Bench marks should be

Observations

301

located on benches so as to ensure safety for an observer. Control bench marks are provided at the ends of profile lines. During the construction of an observation station, at least three initial bench marks are established so as to guarantee their preservation. Control bench marks of all lines are connected to the initial bench marks. Mine-surveying observations at stations include the following procedures: levelling of all bench marks, including control bench marks; measurements of spacings between the bench marks by controlled tension steel tapes (with recording the temperature during measurements); instrumental surveying of particular benches, muck piles, bedding elements, ting, existing displacements, etc. All measurements should be made with checking. The accuracy of measurements should satisfy the following conditions: (I) in geometric levelling, the difference of two measured elevations should be not more than 3 mm; (2) in measuring the spacings between the bench marks, the discrepancy of two measurements should be not more t:han 2 mm; (3) in trigonometric levelling, the difference between two measurements of the same elevation should be not more than 5 mm for lengths up to 10 m or 8 mm for lengths above 10 m. The results of measurements are presented in the following graphical documents: the plan of an observation station (Fig. 12.4)on a scale 1/500, 1/1000 or 1/2000 which should show profile lines, mining workings, the situation and relief of the land surface; vertical sections for each profile with the positions of a flank at the moment of laying out a profile line and during a given series of observations; vector diagrams of bench mark displacements in the vertical plane on a scale 1/1, 1/5, I/lO or 1/20; and the diagrams of the rates of bench mark movement in the directions of these vectors. In observations on landslides, it is also

302

Fig.

Ch. 12. Stability

12.4

Plan

of observation

station

of Quarry

Flanks

required to determine the position of a slip surface in the body of a slope and establish the cause of its appearance. When the results of observations are analysed on profile lines, it is assumed that all displacement vectors of individual points on the slip surface coincide with the movements of the points of the slope surface which are located on normals to the slip surface. Then, having determined the displacement vectors from the results of mine-surveying observations, it is possible to determine the position of a slip line. The position of a slip surface is found in the following manner (Fig. 12.5): (I) the profile of a slope is constructed by the results of observations on the movement of a landslide, and all bench marks and fissures that appeared during the landslide are marked on it; fissures in the top portion and at the foot of the slope should be documented especially carefully; (2) the displacement vectors of bench marks are plotted on a profile, and a perpendicular from the mid of each vector is drawn towards the rock massif; (3) line sections parallel to the displacement vectors of bench marks are laid off on corresponding perpendiculars from the upper

Fig. 12.5 Determining position of slip line by results of observations on displacements of bench marks

~

12.4.

Stability

of Benches

and Flanks of Quarries

12.4. 1TT1nI -J.-J.-+-+--~~

I

I

I

I...

,

t...'

I"

, ,

/

,l".,j"I

,'.

/i

\ v ,

\

II'

)

~

Fig. 12.6 Determinationof angleof internal friction and cohesion by results of surveying of landslide

Stability Benches Quarries

of Working and Flanks

of

In the design, construction and operation of quarries, it is essential to choose a suitable method for calculating the inclination angles of quarry flanks so as to ensure proper stability of flanks and benches, provide place for berms and roads, and achieve a high economic efficiency of mining. There are a number of methods for calculating the flank stability which is estimated in qf a stability coefficient. This is understood as the ratio of the sum of all retaining forces to the sum of thrust forces acting on a landslide wedge:

and lower boundary of a landslide (from the break fissure at the top and from the n = ~F fr + ~F c + A (12.4) line at the bottom). The broken line thus ~Fthr + B constructed is essentially the slip line of the landslide. where ~F fr = j"i:.N i is the sum of friction The results of observations on landslides forces; ~F c = kL is the sum of cohesion can be used for determining the angle of forces; ~F thr = ~ ~ is the sum of thrust forces; internal friction p and the coefficient of f is the coefficient of internal friction of the cohesion k of the rock by the method of rock; k is the coefficient of cohesion deterinverse calculation. mined by the force acting on a unit surface A rock massif at the moment when it loses area; and A and B are some additional balance is assumed to be under the action of retaining and thrust forces. the system of thrust forces ~ and retaining Tensile forces acting in the top portion of a forces: the force of friction tan p1;Ni and the slope produce vertical rupture cracks, beforce of cohesion kL (Fig. 12.6): cause of which the length of the slip surface 1;~ = tan p1;Ni + kL (12.3) decreases.The length of such a crack is found by the formula: where L is the length of the landslide surface 2k cotan (45° -p/2) in the section considered. If-= I"'C\ ~1~.JJ After a certain displacement, the moving y mass of rock stops in a new state of equiliwhere k is the coefficient of cohesion; p is the brium in which the thrust forces are counterangle of internal friction; and y is the mean balanced by the forces of friction. density of the rock. Solving the above equation for this state of In the calculations of the stable position of equilibrium under the action of friction for- d quarry flank on a circular-cylindrical slip ces, we find the angle of internal fric~ion of surface, it is rather difficult to find the centre the rock massif. Substituting the value of p of the most dangerous arc of slip. The into Eq. (12.3),it is then possible to determine analysis of equilibrium of a landslide wedge the coefficient of cohesion k of rock in the gives us only one equation, so that the massif. problem cannot be solved uniquely. Because

Ch. 12. Stability

of this, the centre of this arc is found by the trial-and-error method which involves laborious calculations. It is however possible to use a method which immediately determines the position of the slip surface when the landslide wedge has the least reserve of stability. The method is essentially as follows (Fig. 12.7): (I) a horizontal line BD at a distance H9o from the slope surface and a vertical line AB are drawn on the vertical section of a slope; (2) an arbitrary point D is taken on a line BD and a line at an angle 45° + p/2 to the line BD is drawn from that point (a line DC); a line BC is drawn from a point B at the same angle; (3) a line M K is constructed from the lowermost point of a slope (a point M) at an angle 45~ -p/2; (4) equal sections MP, PP', and P'P" are laid off on the line MK from the point M and equal sections CC', C'C", and C"Co, on a line DC from a point C; (5) lines parallel to the slope line MA are drawn from points P, P', and P" and lines parallel to BC, from points C', C", and Co; the intersections of these lines are points E , E l' E 2' and E 3; a straight line EO is drawn through these points up to the intersection with the line MK; (6) a straight line parallel to DC is drawn

of Quarry

Flanks

from a point a up to the intersection with the line ED (a point E); (7) two perpendiculars are raised to the lines aE and MK respectively in points N and M (Rl and R2 in Fig. 12.7); the intersection of these perpendiculars determines the centre of the circle ing through the points M and E. After these geometrical constructions, a check of the slope stability is made. For this purpose, the landslide wedge is plotted on a larger scale and divided by vertical lines into a number of prisms (Fig. 12.8). The area of each block Si is measured, and the mass of the rock in each prism per metre of the quarry front is calculated by the formula Qi = sir. The vertical lines, which are the boundaries of prisms, are continued downwards to a distance corresponding to the mass of a prism on the given scale. Perpendiculars are raised from the points of the intersection of these lines with the slip surface. After that, N i and 1; are found by the formulae: N i = Qi cos 9; and 1; = Qi sin 9; (values of N i and 1; are given in Table 12.4), and the angle 9; between Qi and N i is measured.

Fig.

12.8

Scheme of landslide

ing slope stability

wedge for calculat

12.5.

Table 12.4

Measures

for Controlling

Landslides

305

popular: flattening out the inclination angles of benches and flanks; leaving safety pillars of Block No. Qi.MN 1;, MN e" deg. N;.MN overburden rock or mineral it.l zones where landslide centres are probable to appear; I 2.33 45 1.65 1.65 decreasing the load on a slope in order to II 2.91 39 2.26 1.83 diminish the forces developed by the active III 2.72 27 1.24 2.43 pressure prism; removing the rock from proIV 1.97 20 0.67 1.85 bable centres of landslides; and strengthening V 0.75 7 0.74 0.09 artificially the rocks in the massif. 8.93 5.48 In undertaking measures for the prevention of landslides, it should be distinguished The length L of the slip surface is then between the cases when the slip surface is found, after which the stability coefficient is distinctly pronounced in nature (along cleacalculated by the formula: vage planes, layer s, etc.) and when it tan pI:N i + kL (12.6) is a merely imaginary line. In the former case, n= the slip surface can be represented by weak 1:1;; s in a rock bed dipping towards a where p is the angle of internal friction, working. Slip surfaces can also along the degrees;k is the coefficient of cohesion of the interlayers of clays and loams in a homogerock; and L is the length of the slip surface. neous bed of rock in a slope or along the The forces A and B (see Eq. 12.4) are not s of inundated rocks. considered here. In the latter case, the position of the slip If the calculated stability coefficient is surface cannot be detected visually and is greater than or equal to the specified value, determined only by survey observations on the flank is considered to be stable, if otherslope deformations or analytically. Such a wise, it is unstable, and it is then required to surface cannot be determined precisely, but flatten out the slope or employ artificial even an approximate determination of its measures for increasing the rock stability. position makes it possible to predict the kind of expected landslide and take suitable protective measures. With a known position of 12.5. Measures for Controlling the slip surface, landslides can be prevented Landslides by one of the methods described below. Landslides in quarries cause enormous Flattening out the slope angle. This method damage to mining plants, disturb the normal consists essentially in diminishing the angle course of mining operations, often lead to of inclination of a slope or bench to a certain large losses of stripped and prepared reserves safe value at which the landslide is imposof minerals, and necessitate multiple transfer sible. The calculation is carried out succesor even haulage of sliding rock masses. sively for a number of different values of an If the working flanks and benches of a inclination angle (Fig. 12.9). The results of quarry are designed correctly, their total stability calculations for these angles are stability will be guaranteed. It is not exclu- represented graphically as a curve 11= .f(a) on ded, however, that local landslide centres will which the angle a corresponding to the appear in certain sections. It is economically specified stability coefficient is found. In the efficient to prevent these local events by example shown in Fig. 12.9,with 11= 1.5, the taking appropriate anti-landslide measures inclination angle of the flank should be 41°. among which the following ones are more Mter that, the mine surveyor calculates the 20-1270

Ch.

306

12.

Stability

of

Quarry

Flanks

less than 18-20°. Underworking of the strata inevitably leads to rock sliding along bedding planes. To preclude a landslide, it is good plan to remove part of the rock mass in advance and thus to increase stability. I 1/

/

'ix

y

~~\~'.4 \:\~k,.. ,,~~

' Q.

> T2

12.6. Artificial Strengthening of Rock Massif Artificial strengthening of slopes in quarries is principally effective in cases when the specified inclination angle a = arctan

AI:h.'

(12.7)

I:a., + I:h.cotano. , I

turns out to be flatter than the angle found from the conditions of slope stability. (In the formula above: hi is the height of a bench; ai is the. width of a berm; and Oi is the incli35 40 45 a. degrees nation angle of a bench slope). Fig. 12.9 Flattening out of slope angle The existing methods of slope strengthening can be divided into the following groups: position of the point corresponding to 11= (1) those based on mechanical principles; = 410 on the top platform of the flank. This (2) those which increase the mechanical point is marked on the ground by a peg and characteristics of rock by the injection of determines the line to which the slope must stren,gthening materials; and (3) those employing durable coatings of slope sections be flattened. Unloading the active pressure prism. When (mainly for rocks liable to quick degradathe mining work is being carried out in zones tion). The first group includes methods in which where deep landslides occur or are probable to occur, the stability of slopes can be slopes are strengthened by bolting, cables, controlled efficiently by unloading the active retaining walls, etc. In the second group, the most popular pressure prism or, on the contrary, by increamethod is the injection of cement slurry. sing the mass of the prism at the foot of the waste dump. The efficiency of this The injections of liquid polymer resins are method can be explained by the circumstance efficient in some cases. In the third group, gunned-concrete, bithat landslides on flank slopes with low inclination angles develop only slowly, so tumen and epoxy-resin coatings are used that there is enough time to transfer a large more often. An artificial coating is often mass of rock from the active prism into the applied onto a metal net or bolting. Each of these methods may be preferable zone of a ive prism ( prism). Removing the centre (locus) of a landslide. over others under particular conditions. For This method gives good results in caseswhen instance, slopes with distinct cleavage planes: tectonic fissures, laminations, disturbance the bed strata are dipping towards the worked-out space and the inclination angle is not zones, etc. can be strengthened reliably by

~

12.6. Artificial Strengthening of Rock Massif

307

as a variety of bolting. Casesare known when flexible cables were arranged in boreholes up to 30 m long. Flexible cables are especially efficient under the conditions when strengthening elements are subjected to bending as well as to tensile stresses. For slopes composed of sand and sand-clay rocks, strengthening methods based on the use of direct-current electric fields are promising. As a d. c. electric field is applied to a rock massif, it causes certain phenomena of electric transfer (movement of electrically charged particles between the field poles). The associated electrokinetic and electrochernical processesgive rise to coagulation and crystallization phenomena which decrease the moisture content of the rock and increase its density, and therefore, strength. It is advantageous to form electric fields in which the lines of force are thickened towards the cathode. This is achieved by arranging the anodes around the cathode. In that case, the strengthened zone in a rock massif acquires the shape of a cylinder with the radius equal to the distance between the unlike poles. In practice, the method of rock strengthening by d. c. electric field is realized as follows. The clusters of holes are drilled in the slope to be strengthened, with the anode holes being arranged around a single cathode hole. The depth of holes should be 10-15 per cent (b)

y

k,V,&/~/~//i

ii,/ J.( j --" (

,

,

¥"

~ Fig. l2.11 Slope strengthening: (b) by flexible cables

(a) by

bolting;

308

Ch. 12. Stability

of Quarry

Flanks

Fig. 12.12 Slope strengthening in quarry flank by do c. electric field

greater than the thickness of the zone of unstable rock. Spacings between the hole clusters are chosen so as to ensure the stability of the entire slope. The scheme of slope strengthening by this method is illustrated in Fig. 12.12. In clays with disturbed or undisturbed structure and a high concentration of finedispersed particles and rather low coefficient of filtration, strengthening rock piles can be formed efficiently by using composition binders. A hole is drilled in the rock massif and filled with a composition binder consisting of cement, quicklime, and clay (for

instance, 40 per cent of Portland cement grade 300 or 350, 10 per cerit of quicklime with an activity 85-92 per cent, and 50-55 per cent of Neogene clay). The composition binder interacts with the rock, so that clays in a certain volume around the hole are dried due to the hydration of the binder, and the associated chemital and adsorption processes lead to the formation of water-resistant and strong calcium hydrosilicates which bind disperse clay particles. With the hole diameter 23 cm, the stre~gthened zone has a diameter up to 50 cm.

Chapter Mine-Surveying

Control

Thirteen of

Mining

Safety

ent seams, and (3) foffi1ation of unprotected zones and zones of elevated rock pressure in seams liable to outbursts. Hazardous zones associated with flooded Modem mining can be characterized by ever increasing depths of mines and accor- workings can in turn be divided into the dingly, more complicated geological and hyd- following types: (a) zones near flooded or rogeological conditions. With an increase in gassy workings in a single seam; (b) those the mining depth, rock pressure increases near flooded or gassy workings in adjacent intensively. Moreover, the cases of sudden seams;(c) zones near flooded workings driven rock, coal, gas and water outbursts, self-igni- in the overburden; (d) those near unplugged tion of coal, etc. are more probable to occur or poorly plugged boreholes; and (e) zones in deeply bedded seams. Under such con- near tectonic disturbances (dislocations). In mine-surveying practice, dangerous conditions, special methods and means are required for carrying out the stoping and prepara- ditions are encountered most often in wortory mining operations, which should be kings approaching flooded or gassy old worstrictly observed and controlled properly to kings. Methods for the construction of safe boundaries and special safety measures of the ensure the safety and efficiency of mining. Under the conditions of elevated hazard of mining work have been developed for each mining, mine-surveying service plays an espe- type of hazardous zone. cially important part and has certain specitics. In many aspects of mining safety, minesurveying service takes the prime role and is 13.2. Control of Mining Work responsible for making decisions which are near Old Workings obligatory for all other mining specialists and When the mining work is carried out near workers. To effect safety control, mine surveyors determine the boundaries of hazard- flooded or gassy abandoned old workings, ous zones and represent them on the plans of special engineering measures should be taken the mining work; inform mine managers and to prevent sudden outbursts of water or gas foremen beforehand when mining workings into the existing workings. In that case, are approaching hazardous zones, participate mine-surveying service has to determine how in the development of safety measures, and reliable are the contours of old workings on survey plans, to calculate the width of barrier observe that these measures are fulfilled pillars (boundaries of safe mining), and plot properly. There are three principal groups of hazard- the pillars on a survey plan. The contour of an old working is conous zones which may be associated with (I) flooded mining workings; (2) formation of sidered reliable if there are the results of mine zones of elevated rock pressure between adjac- surveying obtained upon complete stopping 13.1.

Role of Mine-Surveying Service in Mining Safety

310

Ch. 13. Mine-Surveying

of mining in the working. As a rule, a contour is considered reliable if the old plan of the mining work and field books with the coordinates of theodolite surveys and measurements of workings carried out after the working has been abandoned are on hand. In caseswhen the contour of an old working is not confirmed by mine-surveying documents, it is regardcd as unreliable. Mine-sur\cying service is responsible for the reliability of the contours of flooded workings. With a reliable contour, the boundary of a barrier pillar is established. If the contour is unreliable, the mine surveyor determines the boundary of safe mining work. In coal fields; the width of a barrier pillar, d for seams up to 3.5 m thick and angles of dip up to 30° can be found by the formula: d = 5 m + 0.05 H + 0.002 L (13.1) where m is the extracted thickness of a seam, m; H is the mining depth, m; and L is the length of underground theodolite traverses run from the initial survey points to the contour of flooded workings and the boundary of a barrier pillar, m. The width of a barrier pillar should however be not less than 20 m. In seams more than 3.5 m thick and with angles of dip more than 30°, barrier pillars are not usually left. Instead, as a working approaches an old working, water from the latter is pumped off in due time. For flooded workings driven in the overburden rok, the width of a barrier pillar is determined by the formula: d = 0.05 H + 0.002 L+ Lln (13.2) where H and L are as in formula (13.1); Lln is equal to zero for barrier pillars extended on the strike with the angles of dip of the rock between 0 and 30°; with the angles of dip between 45° and 90°, Lln = 10 m; and with the angles of dip between 30° and 45°, Lln is found by interpolation. For barrier pillars extended to the dip, Lln = 0. The width of barrier pillars near flooded

Control

of Mining

Safety

vertical shafts, pits, and large-diameter boreholes is taken not less than 20 m in all directions and can be determined by the formula: d = 0.05 H + 0.002 L+ 5 (13.3) where H is the depth of a shaft to the mining level on which the barrier pillar will be left, m; and Lis the same as in formula (13.1). The boundaries of safe mining work should be determined by considering the materials of the geological structure of the flooded portion of a mine field, stored in the mine-surveying department of a mining plant, geological parties, archives, etc., the calculations and graphical documentation of the period when the working was in operation, and other information. Depending on the available materials, it is possible to determine approximately the error of the contours of flooded workings and to establish the boundary of the zone safemining work. As a rule, the dimensions of that zone may vary from the width of two barrier pillars up to 200 m or sometimes 300 m. Measures for ensuring safe mining work in hazardous zones should solve the principal problems of organization and give engineering solutions and for effecting of these measures and their control. A typical example of such measures is an optimal scheme of the arrangement of unwatering and advancing boreholes. The number, length and direction of advancing boreholes should be such as to preclude the breakthrough of a new working into an old one. The calculation of the expected water inflow for an unwatering borehole can be done by the formula:

(13.4)

where Q is the expected water inflow to the hole, m3/h; b is the hole diameter, m; His the height of a water column above the hole

13.3.

Calculation

and Construction

mouth, m; 9 = 9.8 m/s2 is the acceleration due to gravity; and 1is the length of a hole, m. The mouths of unwatering and advancing boreholes should be packed hermetically. By the most popular method of packing, a guide tube is inserted into a hole drilled to a depth of 10-15 m and fixed in place by a cement slurry. A gate valve is mounted on the tube, and the whole system is tested for strength and tightness by pumping in water into the hole at a pressure exce~ding 1.5 times that in flooded workings.

of Dangerous

Zones

311

contour of flooded workings is 1800 ill on the airway level 350 ill and 3200 ill on the haulage level 450 ill. In accordance with formula (13.1), the width of a barrier pillar on the airway level is: dl = 5 x 1.5 + 0.05 x 350 + 0.002 x 1800 = 28.6 ill and that on the haulage level is: dl = 5 x 1.5 + 0.05 x 450 + 0.002 x 3200 = 36.4 ill

On the horizontal projection (Fig. 13.1), the sections of length dl = 28.6 ill are laid off 13.3. Examples of Calculation from points 1 and 2; the points l' and 2' thus and Construction obtained define the boundaries of a barrier of Dangerous Zones pillar on the strike on the airway level. At the Calculation and construction of a barrier level 450 ill, the sections of length dl = pillar in a seam with flooded workings. Sup- = 36.4 ill are laid off from points 3 and 4; the pose that a worked-out field in a seam 16 resulting points 3' and 4' give the boundary 1.5 m thick and an angle of dip of 20° is of a barrier pillar on the strike on the haulage flooded at a depth of 350-450 m from the level. Earth's surface (Fig. 13.1).The contour of the To find the pillar boundaries on the dip of mining work (1-2-3-4) is reliable. The length a seam, the horizontal projection of dl, i. e. dl of mine survey lines for determining the cos v = 36.4 cos 20° = 34.2 ill is laid off from the points 3 and 4. The resulting points 311 and 4" determine the boundaiy of a barrier Vertical section across the strike pillar on the dip. The contour of the barrier Level 350 m pillar at flooded workings in the inclined I. tI\.,\.~11' £,e"311' 6 seam field 16es through points 1'-2'-5-6. \v=20' It is depicted on the plan of the mining work. Calculation and construction of a safety Level 450 m pillar under flooded workings. Let a seam 14 Plan 2 ill thick be bedded along a normal at a 6 ~dl=2B.6 m distance of 25 ill under a seam 16(Fig. 13.2). 4li~ E- Id2=36.4m The seam 14is expected to be worked out in ~ "'1" one or two years. Since it is bedded along the "' " normal under the seam 16 in which the workings are flooded, in order to prevent water inrush from the seam 16into 14,a safety 3. 'to i,,- 3" pillar is constructed at a distance not less =28.6m than 40 times the seam thickness. The proI Jd2=36.4m 5 2 tected area is represented by a contour 1'-2'3' 5-6 which confines the flooded workings of Fig. 13.1 Graphical construction of barrier pillar the inclined field together with a barrier at flooded workings pillar. The construction of the safety pillar is

l

312


Control

of Mining

Safety

Fig. 13.2 Graphical construction of safety pillar under flooded workings of overlying seam

carried out by using rupture angles. For the conditions considered, the rupture angles are: ~' = 64°, y' = 70°, and 0' = 70°. The points I' (2') and 5 (6) are projected from the plan onto the vertical section across the strike, which gives points 11 (21) and 51 (6J and onto that on the strike, which gives points 1',2.: on the level 350 ill and points 51, 61 on the level 450 ill. In the section across the strike, lines are drawn from the points 11 (21) and 51 (6J at angles ~' = 64° and y' = 70° respectively up to the intersection with the seam 14.Points 71 (8J and 91 (IOJ found in this way determine the boundaries 9f a safety pillar on the rise and on the dip. Mter that angles 0' = 70° are laid off from the points 1',2', 61, and 51 on the levels 350 ill and 450 ill on the vertical section on the strike. The resulting points 11, 81,91, and 101 in the seam 14define the pillar

boundary in that section. The points 71, 81, 91 and 101 are projected from the sections across and on the strike onto the plan. This gives the general contour of the safety pillar (hazardous zone) in the seam 14' which is confined in the plan by the contour with corner points 7-8-9-10. Calculation and construction of a barrier pillar near an unplugged prospecting borehole. A prospecting borehole is drilled through a seam [6 at a depth of 320 m and stopped in 7 m after ing out from the seam (Fig. 13.3). The position of the borehole in the seam [6 is determined by the measurements of the hole curvature. A seam [4 is bedded at 40 mbelow the normal, The seam thickness is: [6 = 1 m and [4 = 0.9 m. The total extension of mine-surveying theodolite traverses is 4 km in the seam [6 and 5.5 km in the seam 14.

13.3. Vertical

section

Calculation

and Construction

~/""')Y

/~/AW/~

d16=29m

/ ~

/~

~ 7m

'1'*'---

:..: 6

sea((\\&

seali\14

w '

iI-J

I 1 ~' "5' O ,

B

~

~

5

¥

.. II arrlerplar

in seamJ6

I dt4=31.5m I Barrierpillar

I

, I

I

Inseam [4 -from

-the '1B' +

~ ~

I ~

4

Zones

313

deteffilines in plan the contour of the barrier pillar in the seam 16. Since the borehole has been stopped in the underlying rock at a depth of 7 m below the seam foot, the actual distance from the seam 14 is 33 m. Since, however, the safe distance between the seamsis 40 times the thickness of the seam 14, i. e. 40 x 0.9 = 36 m, and the

across the strike

Hole No.100 //$/

of Dangerous

B

Fig. 13.3 Construction of barrier pillar near unpluggedcurved borehole By fofl1lula (13.1), the width of a barfler pillar will be: for the seam 16: dl = 5 x 1.0 + 0.05 x 320 + 0.002 6 x 4000 = 29 ill and for the seam 14: dl = 5 x 0.9 + 0.05 x 360 + 0.002 4 x 5500 = 31.5 ill In the vertical section across the strike, llne sections equal to half the pillar width, i. e 14.5 ill are laid off from a point 01 in the seam 16 on the rise and on the dip. The resulting points 1 and 2 fix the barrier pillar boundary. These points are then projected onto the plan (points I' and 2'). The sections of the half-width of a barrier pillar are again laid off from the point 01 along the strike line ing through the intersection of a borehole with the seam 16,which gives points 3 and 4. These points define the pillar boundary on the strike. After that, points I', 3, 2', and 4 are connected by a smooth curve which

actual distance between the borehole bottom d h 1 . II ...

an t e seam 4 lS sma er, it lS reqwre d to leave a barrier pillar in the seam 14. For constructing this pillar, a noffilal is drawn

... the hole bottom to the mtersectlon with seam, which gives a point O2. The sections of a length dl /2 = 15.75 m are then laid off from that point on the rise and on the dip, which gives points 5 and 6. Similarly, the points 5 and 6 are projected onto the plan to obtain points 5' and 6'. Mter that, the sections of length dl/2 = 15.75 m are laid off from the point o24in the direction perpendicular to a line 5'-6', which gives points 7 and 8. Finally, the points 5', 7, 6', and 8 are connected by a smooth curve which defines the contour of the barrier pillar in the seam 14. Arrangement of advancing boreholes when approaching flooded old workings. When a working is approaching flooded old workings, the mine surveyor develops the scheme of the arrangement of advancing (unwatering) boreholes and determines the number of holes from the following considerations: the probability of the breakthrough of a new working into the old working should be completely precluded; the distance from advancing boreholes to the flooded old working in the section considered should not exceed the width of the crushed edge zone of a barrier pillar in stope workings, i. e. 5 m; the pitch of the advancement of the working should be chosen so as to ensure a constant (not reducing) advance of the prospected portion of the boundary of safe mining work, but not less than the width of the barrier pillar.

314

Ch. 13.

rI...

Mine-Surveying

Control

~

iui!

,..

~1 Reserve

ventilating

B

F:==:=-

.,{'

~

=3 entry

in seam

m4

Safety

2=5m -~ij~~~r~~~d

11=2m ~rr'-

d= 20m

~T "~j',of Mining

I' 87.1

1"'"-

~O\e

---Hole ~!

le

--

~0.'3

-

I

\",.0--

u

1=50m d= 20 m

"

E o "' II ...

Seam m4 iL

d=20~ ~

m=l.omTIO° -.,---

4 Fig. 13.4 Arrangement of advancing boreholes across barrier pillar

When driving a single working in the hazardous zone in a seam with flooded workings, a fan of diverging advancing boreholes is drilled. Consider a case of the arrangement of advancing boreholes when driving a single working in the hazardous zone with the width d of a barrier pillar 20 ill (Fig. 13.4). The planned ventilation adit in a seam m4' boundary of the hazardous zone (I-II), and the boundary of a pillar (1-2-3-4), where water inrush is probable and which should be proved by advancing holes, are plotted on the plan of the mining work. Lines 1-2 and 3-4 are drawn at a distance d = 20 ill frOm the axis 9f the projected working. The first borehole (No. 1) is directed along the axis of the projected working (ventilation adit in a seam m4)' and its optimal length is 50 ill. The second borehole (No.2) is directed into a point which ensures the control of a band of width 12= 5 ill. For this, the shortest possible distance to the flooded working (11= 2 ill) is laid ofTfrom a point 1, which gives a point A. The zone of the crushed edge portion of a barrier pillar 5 ill wide is constructed from the point A. An arc of radius 5 ill is drawn by comes from the point A, and the bore-

2 .,

-;d"ge

Jl

-1~

hole is directed along ;1 tangent to this arc. Considering the distance between the bottoms of boreholes No.1 and No.2, the number of additional advancing holes is determined, noting that a distance of 5 m at both sides is controlled by each borehole and that the entire zone controlled by a borehole should be not wider than 12 m. In the example considered, it is required to drill an additional borehole (No.3). In a similar way, the directions and number of boreholes for controlling the hazardous zone on the dip are determined. Thus, five holes are drilled from the point of the first setting of a drilling rig (a point Bl). The place for drilling another group of boreholes is determined from the condition that the working face should be stopped in a point B2 which is spaced from the point Bl at a distance d = 20 m. The number of advancing boreholes in the second and subsequent groups diminishes by one both on the rise and on the dip of a seam. Arrangement of advancing boreholes at distortions intersecting flooded workings. When mining workings are approaching the distortions which intersect flooded old workings, exploratory drilling should be

1 3.4.

Construction

of Zones

made. This is done for determining the degree of inundation of a dislodger zone and for preventing the probable water inrush, since the disturbed rocks in the distortion zone are considered to be flooded and, when establishing the boundaries of a hazardous zone, are equated to flooded old workings. The width of the hazardous zone at a discontinuous geological disturbance (distortion) is determined in each particular case depending on the accuracy with which the disturbance is represented on the plans of rocks, gypsometric plans, and geological sections. In all cases,however, the boundary of the hazardous zone should be at a distance not less than 30 m along a normal to a dislodger. If the dislodger of a discontinuous geological disturbance has been opened and intersected by preparatory workings and it has been established that the inundation of the rock in the disturbed zone is insignificant, the width of the hazardous zone can b~ calculated by formula (13.1), but it should be not less than 20 m. If the intersection of distortion and flooded workings gets into the zone of rock displacement by the future stope working, the width of the hazardous zone is increased so that the distance along a normal from the seam to the dislodger is not less than 40 m, where m is the seam thickness. The width of the hazardous zone in this case can be determined by the formula: 40 m cos v (cotan d=

v cotan

O + cos ro) sin A

cotan v cos (I) -cotan O

where d is the distance in a plan along a normal from the line of the intersection of a seam and dislodger to the boundary of a hazardous zone; v is the angle of dip of a seam; O is the angle of dip of a dislodger; (I) is the plan angle between the lines of dip of a dislodger and seam; and A is the plan angle between the line of dip of a seam and the intersection line. With a working approaching a discontinuous distortion which intersects a flooded working 1 (Fig. 13.5), two

of

Elevated

Rock

Pressure

315

Fig. 13.5 Arrangement of advancing boreholes for a working approaching geological distortion

advancing boreholes 2 are usually drilled. One of them is arranged normally to the plane of a dislodger and the other is drilled horizontally along the axis of a working. Places for the arrangement of advancing boreholes are determined by the boundary of a hazardous zone. Barrier pillars in mines in an upper seam being worked or in underlying seams located at a distance along a normal not less than 40 m from overlying seams (where m is the extracted thickness of an underlying seam) can be calculated by formula (13.1). In such cases, L is found by considering the total extension of theodolite traverses from the adjacent shafts to the barrier pillar. If the distance along a normal between the adjacent working seams is less than 40 m, the barrier pillar in the underlying seam is constructed as a safety pillar under flooded workings. The protected area is taken as the boundary of the barrier pillar in the overlying seam. 13.4.

Construction of Elevated

of Zones Rock Pressure

Operations in stope workings can cause the deformations and displacements of rocks. The displacement process can influence the state of the rock massif and coal seams.The seam being extracted is bedded in a suite in which one or more seams have already been worked out earlier and coal pillars have been

~

316


left, so that the projections of these pillars get into the displacement zone on the seam being worked out. This gives rise to an additional effect which is called the bearing pressure and forms a zone of elevated rock pressure. It is distinguished between three types of zones of dangerous effect of pillars and edge portions of adjacent seams. The zone of elevated hazard is characterized by a sharp loss of stability of rocks in the roof, in the first place, immediately above a working. Dynamic effects of rock pressure can be observed, such as instantaneous destruction of the rock massif around a stoping face. These effects can raise catastrophically the load on the s and often lead to rock bursts in stoping faces. Strong swelling of ground and squeezing of coal can often occur in the zones of elevated hazard. The dangerouszone can be characterized by a reduced stability of the lower layers of a roof in the worked-out seam owing to increased fissuring and stratification. This usually leads to roof rock inrush and sometimes to rock bursts in stoping faces. The prediction zone has no noticeabe effect on the lining of stoping faces, but the local changes of the stability of the lower roof layer and phenomena of secondary subsidence of the main roof are possible. The dimensions of influence zones under various conditions of seam underworking (or overworking) are determined by the distance of influen~ of pillars and edge portions and by the influence angles. The boundaries of zones of elevated rock pressure are constructed graphically on vertical geological sections perpendicular to the boundaries of pillars or edge portions of a seam. Pillars and edge portions of seams may be in a different position relative to the line of a stoping face. In this case, pillars are understood as non-extracted portions in adjacent coal seams,which have a width up to 2 1,whereas the portions of a width more than 2 1 are regarded as the edge portions of a seam (here

Control

of Mining

Safety

la)

-4

3

'1

I

~ 1

.. 'I~...

1..fJ

~ ~

~I (b)

O

0.4

08

1.2

04

08

12

1,6

all

t6

all

NILr 5

3

0

Fig. 13.6 Nomograms to determine distance of influence of zones of elevated rock pressure in faces: (a) under pillars or edge portions; (b) above pillars or edge portions; 1 -zone of elevated hazard; 2- dangerous zone; 3- prediction zone (solid lines for perpendicular pillars and dotted lines for parallel ones)

I is the width of the zone of bearing pressure). For the pillars of a width less than 2 I. the boundaries of dangerous zones are not constructed. The dimensions of zones of elevated rock pressure in stoping faces driven under pillars (edge portions) can be determined in the nomogram 2 in Fig. l3.6a and of those driven above pillars, in the nomogram 3 (Fig. l3.6b). For constructing the boundaries of the zone of elevated rock pressure, the following characteristics should be known: the bedding depth H of the seam in which a pil)ar or edge portion is left; the extracted thickness m of that seam; the thickness h of the interlayer between the worked-out seam and the seam in which a pillar or edge portion is left; the width a of a pillar; the width I of the zone of bearing pressure in the seam with the left

~

13.4.

Construction

of Zones

of Elevated

Rock

Pressure

317

N Ii is found in the nomogram (here N is the distance of influence, m). In the nomograms of Fig. 13.6, curves 1 correspond to the boundary of influence of zones of elevated hazard, curves 2 to the distance of influence of dangerous zones, and curves 3 to prediction zones. To change from the dimensionless ratio N Ii to dimensional N, this ratio should be multiplied by I, the width of the bearing pressure zone. Mter that, a vertical section through the given pillar is plotted (Fig. 13.8) on which the seam of influence and the worked-out seam, the pillar (or the edge portion of a seam), and the position or a stoping face in the worked-out seam are shown. The calculated distances of influence of the zones of elevated hazard, dangerous zones and prediction zones are laid off in the roof and foot of the seam of the pillar perpendicular to the bedding plane. Then, lines parallel to the influence seam are drawn through the points obtained (3-4, 5-6, 7-8, 3'-4', 5'-6', and 7'-8').

50 40 30 20 10

40

80

120

160 200

7

240 Hm

8

Fig. 13.7 Norn.ograms to determine width 1 of bearing pressure zone: (a) for depths 200-1200 m; (b) for depths 20-280 m

pillar or edge portion. The last characteristic can be found in the nomograms of Fig. 13.7. The zones of elevated rock pressure are constructed in the following way. For the known mining depth H and seam thickness m, the width I of the zone of bearing pressure is found in the nomogram of Fig. 13.7. For instance, with H = 750 m and m = 2 m, the width of the bearing pressure zone is I = 65 m. On the nomogram of Fig. 13.6, the distance of influence of the zones of elevated rock pressure is then determined. For this purpose, the width of a pillar, a, is divided by the width of the bearing pressure zone, I, which gives the dimensionless ratio all according to which the dimensionless ratio

DZ

~ Seam

'8

Seam

I

Seam

I

"

!I

E HZ \

A

,1

\

p oll I

ar

I

~

B 10

!

10'1

Fig. 13.8 Construction pressure from pillar

'~

of zones of elevated rock

318


As an example, let us determine the zones of influence of elevated rock pressure in the roof and foot if the width of the zone of bearing pressure is 1 = 65 m and the width of the pillar is a = 50 m. The ratio of the pillar width to the width of the bearing pressure zone is a/[= 0.77. Using this ratio, we find N /I for faces ipg under pillars (N 1// = 2, N fl = 3.4, and N 3/[ = 5) and for those ing above pillars (N'1/1= 3.5, N~/l = 4.9 and N~/l = 5.9). The distance of influence of a pillar for underlying faces will be as follows: for the zone of elevated hazard: N = 1 = 65 x 2 = 130 m; for the dangerous zone: N 2 = 65 x 3.4 = 221 m, and for the prediction zone: N 3 = 65 x 5 = 325 m. For overlying faces we have: for the zone of elevated hazard: N'l = 65 x 3.5 = 227.5 m, for the dangerous zone: N~ = 65 x 4.9 = 318.5 m, and for the prediction zone: N~ = = 65 x 5.9 = 383.5 m. For the construction of zones of elevated rock pressure from a pillar (see Fig. 13.8), lines are drawn from points 1 and 2 at an angle of 60 o to the bedding plane up to the intersection with the line of distance of influence of elevated hazard zone in points 3 and 4 (3' and 4'). Perpendiculars to the bedding plane are then drawn from these points up to the intersection with the lines of distance of influence of dangerous zone and prediction zone in points 5 and 6 (5' and 6') and 7 and 8 (7' and 8'). To determine the side boundaries of the elevated hazard zone, sections 1-9 (1'-9') and 2-10 (2'-10'), each 20 m long, are laid off in the bedding plane from points 1 and 2 (I' and 2'). Points 9 (9') and 10 (10') are connected with points 3 and 4 (3' and 4') by lines which define the side boundaries of the elevated hazard zone. For a seam [8' the width of the elevated hazard zone is equal to (AB) and for a seam [4' to (CD). The construction of the boundaries of the zones of elevated rock pressure from the edge portions at the side of the worked-out space is done in the same way as for the pillar, but at the side

Control of Mining Safety

of the rock massif. The boundary of the zone of elevated rock pressure is a straight line drawn perpendicular to the bedding plane at a distance corresponding to the width of the zone of bearing pressure. If a number of coal seams are being mined under (above) pillars, the boundaries of the zones of elevated rock pressure are constructed for each seam. If pillars have been left in a number of seams under (above) the seam, being mined, the boundaries of the zones of elevated rock pressure are constructed for each pillar. If the zones of elevated rock pressure from a number of adjacent seams overlap on the seam being mined, they are considered in the first place by the degree of hazard. 13.5.

Construction of Dangerous Zones for Mining Work in Seams Liable to Coal, Gas and Rock Bursts

The mining work in deeply bedded coal seams increases the risk of harmful and dangerous effects of rock and gas pressure which, may be associated with dynamic phenomena: sudden bursts of coal, gas and rock. Soviet scientists have studied the nature of the principal engineering and geological factors causing gas-dynamic phenomena and rock bursts, established the relationships between the effects of gas and rock pressure, determined the parameters for the construction of dangerous zones, and developed the measures for preventing outbursts. One of the main methods for preventing sudden outbursts is working out of protective seams. A protective seam is a seam (or interlayer, or rock layer) which, when being worked out, ensures complete safety from outbursts in another seam of a suite that is to be protected, or relieves partially the rock pressure. In mining of a suite of seams which are dangerous in outbursts, a non-dangerous protective seam is extracted in the first place.

13.5.

Dangerous

Zones

in Seams

Liable

to Bursts

319

Upon the extraction of this seam, the rock pressure in the massif decreases due to the displacement of underworked rock volumes. Protective seams should be worked out without leaving coal pillars. The duty of mine-surveying service in this case is to construct the protected zones and zones of elevated rock pressure, depict them on the plans of the mining work, and inform miners and foremen when workings approach to dangerous zones by 20 m. For seams liable to coal and gas outbursts, the protected zones and zones of elevated rock pressure are constructed on the basis of the following initial data: mining depth H in the protective seam; extracted thickness m of the protected seam; angle of dip v of the Ream; concentration 11, per cent, of sand

(cl

I' I

[i 'Q1

r 2 I~

~

Fig. 13.9 Construction of protected zone in working of protective seam on dip: (a) section on strike with b < 2~; (b) section on strike with b > 2~; (c) section across strike; l-protective seam;2 and 3- seams to be protected; 4- protected zone; 5- zone of dangerous loads

~


320

Control

of Mining

Safety

Table 13.1 Depth

of work m

Values

H,

Values of S~, m

of S:' m

Smallest dimension, a or b, of working in plan, m (refer to Figs. 13.9 and 13.10)

300 400 500 600 800 1000 1200

Smallest dimension, a or b, of working in plan, m (refer to Figs. 13.9 and 13.10)

50

75

100

125

150

175

200

250

50

75

100

125

150

200

250

70 58 50 45 33 27 24

100 85 75 67 54 41 37

125 112 100 90 80 57 50

148 134 120 109 90 71 63

172 170 154 138 117 100 92

190 155 142 126 103 88 80

205 182 164 146 127 114 104

220 194 174 155 135 122 113

56 40 29 24 21 18 16

67 50 39 34 29 25 23

76 58 49 43 36 32 30

83 66 56 50 41 36 32

87 71 62 55 45 41 37

90 74 66 59 49 44 40

92 76 68 61 50 45 41

on the strike. It is required to take into consideration only pillars whose dimensions exceed the following values: 4 m for the seam thickness up to 1 m; 3 m for the seam thickness from 1 m to 2.7 m, and 8 m for the seam thickness above 2.7 m. The dimensions of the protected zone in the roof, SI' and in the foot, S2 (Fig. 13.9)can be determined by the formulae: SI = ~1~2S'1and S2 = ~1~2S~ (13.6) where ~I is a coefficient depending on the method of roof control:

this is done by using protection angles O and pressure angles

=

[31L;

(13.7)

where L; is to be found on a nomogram (Fig. 13.11b). ma The permissible maximum and minimum but should not be less than unity; mo is the values of advancement of the stoping face in critical thickness of a protective seam which the protective seam relative to the mining can be found in the nomogram of work in the seam being protected (Figs 13.9 Fig. 13.11a; ~2 is a coefficient considering the and 13.10) are given in Table 13.3. Construction of protected zone. The protecconcentration 11, per cent, of sandstones in tive seam is worked out at a depth of 1000 m, the interlayer: the extracted thickness is m = 0.7 m, and the ~2 = 1 -0.4(11/100) angle of dip v = 50°. The inclined height of a level is 150 m and the size of the worked-out and S'I and S~ are taken from Table 13.1. If hI < SI in underworking or h2 < S2 in space on the strike is 650 m. A pillar 15 m overworking, it is required to separate sec- wide is left on the airway level. The roof is tions where dangerous loads can appear again; controlled by complete pneumatic back-fil~1

=

mef

13.5.

Dangerous

Zones

in Seams

Liable

to Bursts

321

(a)

(b)

"'"

., L3

b,

.1

--if

4

?

H , 1

"{45~: "'

2

/i

;.:,

~\

t

~ b2~!~ Fig. 13.10 Construction of protected zone in working of protective seam on strike: (a) section across strike with a < 4 + ~; (b) section across strike with a >4 + ~; (c) section on strike; I-protective seam; 2 and 3- seams to be protected; 4- protected zone; 5- zone of restoration of dangerous loads

ling. A seam dangerous in rock bursts is bedded in the ground at a distance h2 = = 10 m. The interlayer contains 50 per cent of sandstones. Since the size of the pillar between the levels is greater than 4 m, then a is taken as the inclined height of a level, i. e. a = 150 m. The size of the protected zone towards the foot of a protective seam is: S2 = f31f32S~ 21-1270

According to the nomogram (Fig. 13.11a), with a = 150 m and H = 1000 m, the critical thickness is mo = 0.68 m. For the roof control by pneumatic back-filling, k = 0.3, and therefore: me! = km = 0.3 x 0.7 = 0.21 m ~1 = me!lmo = 0.21/0.62 = 0.31 ~2 = 1 -0.4(11/lOO) From

Table

= 1 -0.4(50/lOO)

13.1, we find:

= 0.80

S~ = 45 m,


322

Control of Mining Safety

Table 13.2

whence the size of the protected zone along a normal to the bedding plane is:

Angle of Protection angles 0, deg Pressure angles

S 2 = 0.31 x 0.80 x 45 = 11 m

0 10 20 30 40 50 60 70 80 90

63

From find ~ v = 50°; and 230

61

Ll = L'l13l = 180 x 0.31 = 56 m

01

B,

03

04

!P2

<1>3

80 77 73 69 65 74 72 74 70 75

80 83 87 90 90 90 90 90 90 80

75 75 75 77 80 80 80 80 78 75

75 75 75 70 70 70 70 72 75 80

64

64 63 60 59 56 54 52 48 46 43

64

62 60 59 58 56 54 54 54 54

59 57

£2 = £~J32= 230 x 0.8 = 184 m

55 53 52 50 48

N ole: If the direction of stoping work coincides with neither the line of strike nor the line of dip, angle v is taken as the angle of inclination of the seam in a section perpendicular

the nomogram of Fig. 13.11b, we and 1; for jhe inclination angle they are equal respectively to 180 m m. Thus, we have:

to the face direction.

Since a < 4 + ~, the zone of the restoration of dangerous loads cannot form and, according to Table 13.3, the permissible advancement b2 is not limited, and the minimal advancement b~ can be taken equal to 20 m. We find from Table 13.2 that 01 = 70° and 03 = 80°. The construction of zones of elevated rock pressure is illustrated in Fig. 13.12. For the zone of elevated rock

Table 13.3 Pernlissible advancement to prevent rock bursts, m

Mining conditions

Minimal advancement: b; in underworking b; in oveI;;Working Maximal advancement** b1 in underworking b2 in overworking: if a < Ll + L2 if a > Ll + L2

Permissible prevent

advancement outbursts, m

khl h2

h1, but not less than 20 m* h2, but not less than 20 m

Not limited

Not limited

b1 < L3 + h1 cotan b2 < L3 -0.3

~3

Not limited

h2

* Coefficient k depends on the rate of advance of a stoping face in the protected seam: v, m/day k

up to 2 I

2 to 5 1.2

over 5 1.4

** Permissible advancements are given for the stoping work on the strike. If the stoping work is carried out on the dip, LJ and
13.5.

Dangerous

Zones

in Seams

Liable

to Bursts

323

(a) ron

200

/.I\

0.8 1150

III

IIII

100

\ \

0.4

=50m

0

400

800

\

\

H,m

(b)

I~~

t(J&, II

300

, La

250

L~ 200

~

\0

30

60

IXo

y

.,,\

y Fig. 13.12 Zones of influence , of seam edge portion: I -protected zone; 11- unprotected zone; 111- zone of elevated rock pressure

21.

Chapter M ine-Surveying of Geological

Fourteen Control Exploration

the geological structure of the region in view of the collected geophysical and geochemical data and (2) to use the established regularities Geological exploration is essentially a of mineral location in order to find out the cycle of investigations which are carried out most perspective geological structures, evaluin a definite sequence and can be character- ate their prognostic resources, and determine ized by the following stages: further directions of geophysical and geo1. The stage of regional geological recon- logical survey and search. naissance which is aimed at determining the 2. The stage of geological survey and genprincipal bedding characteristics of various eral search is the main stage when large-scale minerals in a particular region so as to make investigations of geological structures are prognostic valuations of the perspectives of carried out in order to distinguish local areas their extraction and outline areas for more and structures which are promising for the detailed geological prospecting. This stage detection of mineral deposits. Geological surcan be divided into two substages: (a) re- veys at this stage should be made primarily gional geological and geophysical reconnais- within the limits of mining areas. The results sance and (b) regional geophysical and geo- of surveys and prospecting at this stage are logical surveys and hydrogeological and represented in the form of geological maps, engineering-geological work. maps of minerals, and prognostic Geological and geophysical reconnaissance maps of mineral location. (the Ist substage) is effected for the formation 3. The stage of geological search is carried of a new or renovation of the existing geo- out in order to detect mineral deposits within logical and geophysical basis which is needed the limits of known and potential ore fields for establishing the principal characteristics and basins of sedimentary minerals where the of the geological structure of large regions previous exploration work has revealed the and the regularities of the location of probability of the detection of deposits. The minerals within their boundaries. search work at this. stage takes place in The results of geological and geophysical boreholes and pits with the use of georeconnaissance are used for plotting geophysical and geochemical methods, rock logical, prognostic and other general and sampling, panning, etc. sheet maps, geological and geophysical key Investigated areas are represented on geosections, and schemesof the geological struc- logical maps which show the regularities of ture of deep levels. the localization of mineral bodies. The main purpose of prospecting opera4. The search-valuation stage is an intertions at the second substage is (I) to analyse mediate stage between the reconnaissance 14.1.

Brief Data Exploration

on

Geological

14.2.

Mine-Surveying

Control

and the exploration of mineral deposits. The main object of this stage is to evaluate the commercial significance of detected deposits, reject. those which are of no interest for the mining industry, and select objects for preliminary prospecting. The results of the search-valuation work are represented in the form of preliminary geological maps and geological sections of a detected deposit. 5. The stage of preliminary prospecting is done in order to obtain trustworthy information for reliable geological, technological and economic evaluation of commercial significance of deposits. Most deposits are explored by prospecting boreholes. The results of preliminary prospecting are represented in the form of approved temporary specifications and technico-economical report on the expediency of the detailed exploration of a deposit. 6. The stage of detailed prospecting (exploration) is carried out only for deposits which are evaluated positively by preliminary prospecting and recommended for commercial exploitation. 7. The stage of complementary prospecting can be fulfilled both on explored deposits which are not still mined commercially and on those which are being mined. 8. The stage of exploitation prospecting is continued during the whole period of mining of a deposit and is carried out for collecting systematic reliable information required for current (annual) and operative (quarterly, monthly, and daily) planning of mineral extraction and the control of the completeness and quality of extraction. The main objects of exploitation prospecting consist in determining more accurately the contours of mineral bodies and their internal structure and bedding conditions, quantity and quality of mineral resources, geometrization of technological types and grades of a mineral, etc. All stages of geological reconnaissance and prospecting are associated with geodetic, to-

of Geological

Work

325

pographic and mine-surveying operations which are done to attain the following objectives: I. The formation of the geodetic basis for the layout, connection and geological survey work required for geological prospecting; provision of a control network for topographic surveys when these are needed; and the solution of various engineering problems when driving mining and exploring workings or making the geophysical and drilling work. 2. The formation of the topographic basis for geological prospecting; this is meant as a topographic plan or map with the points of field observations, which is plotted in a simpler form, i. e. without showing some elements of the topographic situation and relief that are inessential for the construction of geological boundaries. The topographic and geodetic materials collected at the stage of geological prospecting are latt;r used in the design and exploitation of mining plants. 14.2.

Mine-Surveying of Geological

Control Work

The mine-surveying control of geological work includes the following procedures: the transfer of the design positions of objects of geological observation (boreholes, mining workings, etc.) into nature; determination of the planimetric and height coordinates of these objects; and the formation of the topographic basis for geological and other special maps. The geodetic control for the mine-surveying work can be provided by: (a) geodetic nets; (b) elements of survey control, such as planimetric, elevation and combined planimetric-elevation surveying nets and individual points, and geodetic reference nets; (c) distinct contour points of deposits whose coordinates can be found on topo-


326

Control of Geological Exploration

Table 14.1 Root-mean square errors of positions of geological observation objects relative to initial points, m

Stages of geological prospecting

plan

in elevation

90(100) 40(50) 20 (25)

10(20) 5 (10) 2(3)

in

I. Regional geological investigations, geological survey work, and geperal search with compilation of maps on a scale: 1/100000 and smaller 1/50000 1/25000 2. Search work, search-valuation work and preliminary prospecting with compilation of maps on a scale 1/10000 3. Search-valuation work, preliminary and detailed prospecting with compilation of maps on a scale 1/5000 and larger N ole: Numbers desertous,

woody,

in brackets

are rms errors

and mountainous

regions.

for determining

(2) 0.5

the positions

of geological

observation

objects

the accuracy recommended in Table 14.1. The elevations of these objects should be determined with errors not exceeding the following data: (a) in hydrogeological surveys, 0.5 of the adopted interval of hydroisohypses on hydrogeological maps, but not more than twice the error given in Table 14.1; (b) for individual hydro geological surveys for determining the gradients of underground flows, inundations of sections and mining workings (mines, shafts, etc.), within t!!e accuracy for technical levelling, i. e. 50 J L, mm, where L is the length of a geometric level line, km. The coordinates of the mouths of stationary hydraulic boreholes should be determined from the closest bench marks and points of a national levelling net with an rms accuracy not worse than I 10 cm. In geological work, deep geological mapping and general search with the compilation deposits. For the objects of hydrogeological obser- of maps on a scale 1125000 and smaller, the vations, the survey work for determining the objects of geological observations are transplanimetric coordinates should be done with ferred into nature and connected, as a rule,

graphic maps (plans) or aerophotogrammetric plans with the required accuracy; and (d) objects of geological observations whose coordinates are determined with the required accuracy. The mine-surveying control for transferring the design positions of objects of geological observations into nature includes the following steps: (a) the preparation of initial data and the compilation of schemesand the plan of work; (b) measurements for determining the positions of observation objects on the ground; and (c) the fixation of the positions of transferred objects. The accuracy of the determination of planimetric and height coordinates of geological observation objects can be taken by reference to Table 14.1 for deposits of solid minerals and to Table 14.2, for oil and gas

14.3. Topographic

327

Basis of Geological Exploration

Table 14.2 Kind

(category)

of

Ultimate

borehole

transfer into nature

Single reference and parametric boreholes Structural and search boreholes Exploratory boreholes Boreholes on exploited areas Boreholes in water areas

150

errors, m

preliminary determination of elevations of borehole mouths

determination of planimetric position of borehole mouths

detennination of elevations of borehole mouths

150

100

5.0

10

30

1.0

5

12

0.5

4

0.3

10

0.5

50 25 10 20

5

Notes: I. Errors are given relative to the points of a national geodetic net and geodetic densification nets. 2. As initial points of connection, it is possible to use any points including those by which the structural maps are plotted, provided that this ensures the accuracy indicated in the table.

according to the topographic maps and materials of aerophotogrammetric surveys, Instrumental field measurements at these stages of geological work are only possible in exceptional caseswhen topographic maps are unavailable or cannot ensure the specified accuracy of the connecting work. The points of a geodetic net or surveying nets fixed on the ground by permanent bench marks can be used for the layout, connection and geological survey work, planimetric and elevation control of topographic surveys, and for solving certain engineering-geological problems. The points of geodetic survey control fixed by temporary bench marks, points of geodetic reference nets, and distinct contour points on the terrain whose coordinates are taken from a topographic map can be used only for the layout, connection and geological survey work. The coordinates of geological observation objects can be used: for marking the positions of these points on maps and sections with an accuracy that can ensure reliable representation of the results of observations and accurate calculation of mineral resources;for deter-

mining the boundaries of mineral deposits, revealing geophysical anomalies, etc; and for compiling special maps, sections, prospecting profiles, and other graphical documentation. 14.3.

Topographic of Geological

Basis Exploration

The topographic basis for the geological exploration work can be provided by: (a) topographic maps (plans); (b) large-scale plans; or (c) special topographic plans. . In the geological, search and exploration work, the scale of the topographic basis should correspond to that of the map to be plotted. The recommended scales of the topographic basis for preliminary and detailed geological prospecting are given in Table 14.3. In the maps and plans of the topographi(; basis on a scale 1/10000 and smaller, the errors in the positions of contours, orientation marks and horizontals should be not more than 2.5 times the errors permissible in national topographic maps. In special topographic plans used as the

328



Table 14.3 Stage of geological prospec- Scale for topographic sur. ting veying

Preliminary prospecting 1/10000 to 1/5000 Exploration of: (a) metal ores 1/10000 to 1/1000 (b) carbonate rocks, phosphorites, sands, and gravels 1/25000 to 1/5000 (c) salts 1/25000 to 1/10000 (d) coals and oil shales 1/1000 to 1/2000 (e) underground water 1/1000 to 1/5000 (I) other non-metallic minerals 1/10000 to 1/5000

topographic basis, the errors in the positions of land contours and objects relative to the nearest points of a surveying net should. not exceedthe pef111issible errors of corresponding topographic maps by more than 1.5 times for a scale 1/5000 or 2 times for larger scales. The errors of relief surveys relative to the nearest points of elevation control on the topographic basis should not exceed 0.5 m for contour intervals of 1 m or 1/3 of the contour interval in other cases. For better clarity, the amount of topographic details on geological maps on a scale 1/10000 and larger is diminished. Coordinate grids are shown as ticks of kilometre lines in intervals of 10 cm. The points on geodetic nets and on the schemesof geological observations are.taken selectively, i.e. only those points which are essential for the compilation of geological and geophysical maps are used. The points of a national geodetic basis are shown only in caseswhen this is specified by the design. Land relief is indicated by horizontals and numerical marks of individual heights. For the topographic basis on a scale 1/10000, land relief is shown in the same vertical contour intervals as on national topographic maps. For larger scales, the following contour intervals may be recommended: 2.0 m for a scale 1/5000; 2.0 m or

1.0 m for a scale 1/2000, and 1.0 m for a scale 1/1000. For mountainous regions and foothills, the recommended contour intervals are respectively 5.0 m, 5.0-2.0 m, and 1.0 m. Hydrographic objects are indicated on the topographic basis only as the coastal lines of seas,lakes, rivers, etc. without detailed characteristics. Vegetation is not shown. Woods are marked by contours. Swamps and marshes are shown by conventional symbols without detailed characteristics. Other typical features of the terrain and ground are not indicated on the topographic basis. The topographic basis of geophysical maps should give only the situation associated with the text of the report; land relief is shown only in rare cases. 14.4.

Transfer of Plan of Exploratory Workings into Nature

Exploratory workings are transferred into nature according to the plan of the minesurveying work. Depending on local conditions and the specifics of geological prospectiDg, this plan may involve various kinds and volumes of the topographic and minesurveying work. For instance, Fig. 14.1 shows the plan of the topographic and mine-surveying work for detailed prospecting of a deposit by drilling exploratory boreholes along profile lines. The plan envisages triangulation surveys (points I, II, III and IV); running of base lines (main theodolite traverses) for the layout of profile lines; the connection of base lines (by closed theodolite traverses) to triangulation points III and IV; plane;.table surveying of the territory of a deposit on 10 plates; and the transfer and connection of points for borehole drilling. Exploratory workings and objects of geological observations are transferred into nature and connected relative to the points of reference nets which can include main theodolite traverses (base lines), profile lines. and

14.4.

Transfer

of Exploratory

the points of a surveying net and national geodetic net. The layout work is carried out with an accuracy which can ensure the required accuracy of connection. If an object is transferred into nature with an accuracy insufficient for connection, additional connection to the closest control points should be carried out. Networks for detailed geological prospecting usually have a relatively regular geomet-

Workings

Plan into

Nature

329

ric shape and consist of a system of parallel base lines intersected by a system of parallel profiles (Fig. l4.2a). In many cases, some base lines can be matched conveniently with extended objects on the terrain (roads, river banks, open watersheds, etc.). In such cases, base lines may have a curvilinear shape (Fig. l4.2b). As a rule, the plans of exploration nets are transferred into nature by instrumental methods.


330

Control of Geological Exploration (b)

(a)

.-~::. ...Profile Fig.

14.2

Construction

Main traverse with observation points

of base lines and prospecting

In laying out geological exploration nets, the mine-surveying and geodetic work is practically organized on the following principles: (a) the initial points and directions are transferred into nature, and the survey area is delineated by laying out base lines, which provides a 'framework' for subsequent layout operations; (b) the. base lines delineating the survey area are connected to the points of a geodetic net, i. e. the 'framework' is connected to the existing system of coordinates; and (c) profiles are laid out and picked points are established. For transferring the initial points into nature and asg direction to the initial portions of base lines, the following methods can be employed: (a) one of the base lines es through a point of the geodetic reference net existing in the region being explored. In that case, the

profiles

angle between the direction of the base line and the direction onto another point of the reference net (for instance, angle 13,Fig. l4.3a) is measured on a topographic map. This angle is then laid off on the ground by an angle-measuring instrument set up in the initial point; (b) base lines far from the points of a geodetic reference net. Then a point of the reference net near the base lines is selected, from which two or three adjacent reference points are visible, and a theodolite traverse is run between the selected reference point and the base line (Fig. l4.3b). By means of this traverse, the base lines can be connected to the existing local system of coordinates; (c) the region of geological prospecting is located in an inhabited area, so that the points of a geodetic reference net are invisible from it. In that case, the directions of base lines can be assigned by means of a magnetic azimuth. If the prospected region is located in

14.4.

Transfer

of Exploratory

Workings

Plan into

Nature

331

(a)

.,A /

~

--c.

(32

(b)

==

-

~ B.

Fig.

14.3

Scheme

of base

"""6

lines

a closed area with poor visibility (woods, etc.) and where there is a magnetic anomaly, base lines can be' connected by a geographic azimuth. The intervals between the pickets (observation points) on profile lines are measured in one direction by means of range finders or tapes. Inclination angles wider than 5° are measured by theodolites or inclinometers; in such cases a length laid off between the pickets is corrected for the inclination angle. The coordinates of the final pickets of profiles are determined by running theodolite traverses between the ends of profiles. For observation points and exploratory workings not coincident with the points of a reference net, connection can be done by tacheometric or plane-table surveys, length measurements or intersections.

14.4.1.

Connection and Transfer of Geological Observation Objects from Topographic Map into Nature

In the geological survey and search work made on a scale 1/25000 or smaller, geological observation objects are transferred into nature and connected by reading off their positions on topographic maps or aerophotographic maps and plans. For regions with a small quantity of contours and for which renovated maps are not available, the plane coordinates and elevations of geological observation objects are transferred into nature and connected according to the materials of the aerophotogrammetric surveys of the latest years. Objects can be transferred from aerophotographs onto a topographic map by visual, graphical or instrumental methods.


Control

of Geological

Exploration

map; the directions connecting the central points on the transparent paper sheets are matched with the corresponding line of the topographic map. The intersections of like directions determine the positions of the 2' point being transferred on the map. The accuracy of the position of points Fig. 14.4 Transfer of points from aerial photo. transferred by the method of intersections graphs onto topographic map by intersections can be estimated by reference to Table 14.4. The method of resections consists in that at In the visual method, a point is transferred least four reference points are chosen on an by linear intersections from two or three aerial photograph and a topographic map reference points on a map. In that case, the (for instance, points a, b, c, and d on an aerial lengths of corresponding sections on the photograph and points A, B, C, and D on a aerophotographs and map are compared map). A sheet of transparent paper is laid on the aerial photograph, and directions are visually. The visual method is employed in cases drawn from the point to be transferred (say, when the terrain has distinct contours and x) onto the selected reference points a, b, c, only slightly dissected relief. Experience has and d. The transparent paper sheet is then shown that, for transferring of points with the laid on the map so that the drawn directions root-mean square error of I mill, the distance x-a, x-b, x-c, and x-d through the points from reference points to the given object on A, B, C, and D on the map. After that, the maps should be not more than 5 mill for flat point x is punched from the transparent land, 3 mm for foothills, and I mm for moun- paper onto the map. The instrumental method of point transfer tainous regions. The graphical methods of transfer most is the most accurate and least labour-consuoften employ direct intersections from the ming. central points of aerophotographs and resecGeological observation objects can be tions. connected or transferred into nature from a In the method of direct intersections, the topographic map (aerial photograph) by one central points of aerophotographs are first of the following methods. transferred onto the map by the method of photo triangulation. The points to be transferred onto the topographic basis are read off Table 14.4 and punched on two adjacent aerial photo~ graphs. The central points (431 and 432 in Map scale Accuracy of positions of points, mm, for mean difference of elevations between Fig. 14.4) and points to be transferred (say, points, m points I, 2, 1', and 2' in Fig. 14.4) are punched from each aerial photograph onto 50 150 200 500 transparent paper. Then, the directions onto 15000 1.4 2.0 2.7 5.4 the central points and points to be transfer110000 0.6 1.0 1.4 2.7 6.7 red are drawn on the sheets. Mter that, the 125000 0.3 0.4 0.5 1.8 2J sheets of transparent paper are laid onto the 150000 0.3 0.3 0.3 0.5 1.4 topographic basis and oriented so that the 1100000 0.3 0.3 0.3 0.3 0.7 central point of each sheet is coincident with 1200 000 0.3 0.3 0.3 0.3 0.3 the corresponding point on the topographic ~ I 430

431

' 432

14.4.

Transfer

of Exploratory

1. By reading off a point if this point coincides with a contour point on the map. 2. If the given point is located between two contour points on the map, by measurements on the range line of these points from one of the points to the point to be connected (or transferred). 3. If the point to be determined is visible from contour points, its position can be found by direct intersections. 4. If three typical points are visible from the point to be determined and these points are indicated on the map, the position of that point can be found by resection. The determination of the planimetric coordinates and elevations of geological observation objects on topographic maps (aerial photographs) includes the following steps: (a) contours and orientation marks depicTable 14.5 Pattern of terrain and relief

Workings

Plan into

Nature

333

ted on a topographic map are found on the terrain; measurements are carried out, when needed, on the terrain between the objects being determined and the orientation marks; and the objects are indicated on the map; (b) observation objects are transferred from aerial photographs onto a map; and (c) the planimetric coordinates and elevations of observation objects are read off on a map. Measurements on maps and terrain should be carried out by methods which can determine the plan positions of objects relative to a known contour with a root-mean square error not exceeding 0.2 mm on the map being used. The measurements of planimetric coordinates and elevations on maps are made twice. The errors in elevations of observation

Root-mean square errors (m) of elevations determined by interpolation between marked points (numerators) and between horizontals (denominators) map scale

Flat terrain (inclination angles up to 2°) Flat woody terrain (inclination angles up to 2-4°) Flat densely inhabited terrain (inclination angles up to 2°) Hilly rugged (open) terrain with prevailing inclination angles up to 6° Hilly rugged (closed) terrain with prevailing inclination angles up to 6° Foothill and mountainous terrain with prevailing inclination angles up to 15° High-mountainous terrain

0.4-0.8

0.8-1.6

1.2

2.5

5.0

11.0

0.5-0.8

0.8-1.6

1.5

3.0

6.0

12.0

0.4-0.8

0.9-1.6

1.5

3.5

7.0

14.0

0.6-1.0

1.2-2.0

2.5

5.0

10.0

20.0

1.0

1.8-2.2 4.0 8.5 17.0 Error not more than 1.5 of contour interval

33.0

10.0 20.0 Error not more than 2.0-2.5 of contour interval

40.0

334



objects on topographic maps should correspond to the data given in Table 14.5. The determination of the planimetric coordinates and elevations of geological objects on topographic maps should be made with a check of at least 20 per cent of the points being measured.

of the oriented directions from the rotor centre in order to establish deviations and (b) the layout and fixation on the ground of the design direction of boreholes and the determination of the plan position of faces.

14.4.2.

The layout of open exploratory workings (ditches, trenches, etc.) consists in transferring the design position of an axis and side crests of a working into nature. The layout procedure is started by transferring the ends of the axis onto the ground, which can be done by various methods or their combinations depending on the conditions of measurements and the provision of a geodetic basis. These methods have been discussed earlier. On a closed (woody or hilly) terrain it is however more preferable to use the method of a design theodolite traverse. In the plan shown in Fig. 14.5, points K and N are the ends of the design axis of a ditch and A and B are the points of a geodetic basis. In order to transfer the points K and N onto the ground by the method of a design theodolite traverse, it is essential to know angles /3B and /3K and horizontal distances BK = SBK and KN = SKN which can be obtained by solving inverse geodetic problems by the formulae:

Transfer of Geological Observation Objects from Reference Net into Nature

In the geological search and exploration work made on a scale 1/10000 or larger, exploratory workings and geological observation objects are transferred into nature and connected by instrumental methods to the points of a national geodetic net, densification nets, surveying nets, or reference nets. If workings are located at distances not more than 300 m from a reference net, their positions can be determined by a polar method (by a theodolite 01 a plane table), the distances being measured by a range finder. The positions of points near profile lines can be determined by the method of perpendiculars with the distances measured by measuring tapes or range finders. The positions of fixed boreholes and mining workings can be determined by analytical methods relative to the points of a national geodetic net, densification nets, surveying nets or base lines. The work for the connection of geological observation objects includes: (a) the compilation of a connection scheme; (b) measurements for determining the planimetric coordinates and elevations of geological observation objects; and (c) the compilation of the list of planimetric coordinates and elevations of geological observation objects. With directional drilling of boreholes, the following additional operations are made: (a) the layout and fixation on the ground

14.5.

tanaBK

Layout Ditches

=

of

YK -YB

Exploratory

,

XK -xB SBK

---

YK-YB sin

XK-XB IlBK YN

COS IlBK -YK

tanaKN XN

SKN=

YN-YK .= smaKN

13B= aBA -aBK'

XK

XN-XK cosaKN 13K = aKB -aKN

where x K' Y K' X N' and Y N are the coordinates of the points K and N determined graphically

14.5. Layout of Exploratory Ditches

335

(a)

v ~ ~o ~o

0

..inewood

0( 7 PK

v

14.5

Layout

of exploratory

6

v

0

Fig.

. :

v

VI

ditch

on the plan; x B' y B are the coordinates of the point E taken from the list of calculated coordinates of the points of a geodetic net; and aBA is the initial direction angle taken from the list of the calculated coordinates of the points of a geodetic net. A theodolite is set up in the point E and the junction angle 13Bis constructed from a direction EA at two different positions of a circle, after which the length of a line SBK is

laid off in that direction, and the point K thus obtained is fixed. The angle ~K is constructed in the point K relative to a direction KN, the design length SKN of a ditch is laid off, and the point N is fixed. The upper crests of a ditch are laid out by using a number of profiles which are plotted on millimetre-squared paper on a large scale (say, 11200).The width 1 of the ditch bottom



(Fig. 14.5,where it is shown by a dotted line), the depth h, and the inclination angle of ditch sides are taken from the design and the elevations of the points of the Earth's surface, from the plan. In the case considered, three profiles are plotted: a longitudinal profile along the axis KN (Fig. 14.5b) and two transverse profiles through the points K and N (Fig. 14.5c). The construction of profiles gives the points of intersection of ditch crests with the Earth's surface (1, 2, 3, 4, 5, and 6). Inclined distances K-l, K-2, N-3, and N-4 are then found on transverse profiles and K-6 and N-5, on a longitudinal profile. These distances are laid off on the ground from the points K and N; the former four perpendicularly to the ditch axis and the latter two, along the axis. The points 1, 2, 3, 4, 5, and 6 are fixed on the ground. The angles of the upper crests of the ditch (points 7, 8, 9 and 10 in Fig. 14.5) are obtained at the intersections to the continued lines 1-4 and 2-3 and perpendiculars raised to the ditch axis in the points 5 and 6. If the terrain is flat, cross-sectional profiles are not constructed, and the distance from the ditch axis to its crest is determined by the formula: N-4 = N-3 = 112+ d where d is calculated by the formula: d = hltan..

Geodetic Control of Geophysical Prospecting Methods

14.6.1 .General Data on Geophysical Prospecting Methods Geophysical prospecting includes the methods of the investigation of the Earth's crust, search and prospecting for minerals, and engineering geological studies which are based on the analysis of various physical

fields, either existing in nature or formed artificially. Any kind of these fields can be characterized by its specific parameters. For instance, a gravitational field can be represented by the acceleration due to gravity or second derivatives of the gravity force potential; a magnetic field is characterized by the total intensity vector and its components (vertical, horizontal, etc); an electromagnetic field is characterized by the vectors of magnetic and electric components; an elastic field is described by the time of the propagation of various elastic waves; etc. The principal possibility of geophysical methods of prospecting with the use of various physical fields is based on the fact that the distribution of field parameters on the Earth's surface, underground, in air, outer space, and in the Ocean is determined by the general structure of the Earth and the near space, variations in the physical properties of rocks, and the dimensions and bedding depths of geological objects. Geophysics has to solve two types of problems: a direct problem and an inverse one. Since the parameters of physical fields depend uniquely on the properties and dimensions of the geological objects being prospected, the parameters of a field can be uniquely determined when one knows the properties and dimensions of geological objects. This is the direct problem to be solved in geophysics. The inverse problem consists in determining the dimensions, bedding depth and other characteristics of geological objects by the measured parameters of a physical field, which, as a rule, cannot be determined uniquely. The inverse problem can be solved uniquely by studying a complex of fields. Geophysical prospecting methods can be employed in outer space, on the Earth's surface, in seas,and underground. According to the problems and objects of investigation, geophysical prospecting can be divided into regional, structural, prospecting for ores,

14.6. Geodetic Control of Geophysical Prospecting

petroleum and gas, and engineering geophysics. Among the various methods used for geophysical prospecting, the gravitational, magnetometric, electric, seismic, nuclear and geothermal methods are more popular. 14.6.2.

Principles of Gravitational Prospecting

Gravitational prospecting is based on measuring the acceleration due to gravity and its variations (gradients) in different directions. The parameters of the field of gravity force depend, on the one hand; on some factors associated with the shape and rotation of the Earth (normal field) and, on the other, on the density variations of rocks in the lithosphere (anomalous field). The gravitational (normal) field of the Earth is the field of the gravity force which is the resultant of two forces: the force of attraction of the Earth and the centrifugal force caused by the rotation of the Earth on its axis. The force of gravity can be measured in of the acceleration 9 acquired by a freely falling body. In gravitational prospecting, the unit of acceleration is 1 cm s- 2 which is called the gal. Gravitational prospecting is based on measuring the anomalies of the gravity force, i. e. its deviations from normal values. The normal field of the gravity force can be analysed by the formula: Yo =Ye(l-

~sinB-

where ~ = (Yp-Ye)/Y,

~lsin22B)

~1 = (1/8)a2 + (1/4)a~

a is the contraction of the Earth's ellipsoid; B is the geodetic latitude; Yp is the normal gravity field at a pole; and Ye is the normal gravity field at the equator. Thus, the anomaly of the gravity force is essentially the difference between the gravity force observed and its theoretical value which can be calculated by one of the formulae for 22-1270

337

the normal gravity force with the introduction of corrections (reductions). In gravitational prospecting, the most popular formula for describing the inhomogeneous density of the Earth's crust is based on Bouguer's anomaly (Bouguer's effect): AgB = gm -'Yo + Agl + Ag2 + Ag3 where gm is the measured gravity force; Agl is the correction for altitude which reduces the measured value to the sea level (Faye's correction), A 9 1 = 0.308 H (H is the altitude above sea level, m; Ag2 is the correction for the attraction of an intermediate layer, which is equal to the attraction of the masses located between the sea level and a real surface, Ag2 = 0.0419 o-H (0- is the mean density of rocks in that layer and H is the altitude of an observation point); and A g3 is the correction for relief. The relief correction takes into the deviations of the physical surface of the Earth from the horizontal plane ing through the given point. For calculating the relief correction, the portion of the Earth's surface around the point of observation is divided in a particular manner into a number of areas so as to approximate the relief by simple geometric bodies whose gravitational effects can be determined analytically. The correction for the surrounding relief is calculated for particular annular zones arranged concentrically around a gravimetric point. Since the shape of the relief in each zone may be variable, these zones are divided further into curvilinear prisms. The actual (physical) surface of the Earth within each prism is replaced by a horizontal plane whose altitude is equal to the mean altitude of the prism relative to the observation point. The effect of the terrain on the topographic correction decreases proportionally with an increase in the distance from the observation point, because of which the entire region for which the correction is taken into is divided into three zones: the closer (up to

338



200 m), the mid (from 200 m to 2000 m), and the farther (from 2000 to 13000 m). The highest effect is produced by the relief elements in the closer zone. In some cases,a central zone of a radius of 10-50 m is separated in the closer zone. In high-precision gravimetric surveys, the relief corrections in the mid and closer zone are determined by instrumental methods.

sections composed of horizontally bedded or gently dipping structures; and (3) underground electric prospecting used for the detection of geoelectric inhomogeneities between the boreholes or underground workings and the Earth's surface. Electric prospecting deals with the following kinds of field: I. Local natural electric fields, including those of electrochemical and electrokinetic origin. Electrochemical fields can be caused 14.6.3. Electric Prospecting by oxidation-reduction reactions at boundaThe electric methods of geological prospec- ries between the electronic conductors (ore or ting are based on studying natural and mineral bodies) and ionic ones (underground artificial electromagnetic fields in the Earth's water surrounding an ore body). Electrocrust. Natural fields may be either permanent kinetic fields exist due to the filtration of or variable in time. The former are conven- underground waters through porous rocks and the associated processesof diffusion and tionally called electric fields and the latter, adsorption of ions on solid particles. electromagnetic. In electric prospecting, both normal and 2. Regional natural electromagnetic fields anomalous fields are studied. Normal fields (called magneto-telluric fields) which appear are those which exist above a semispace in the Earth's crust in the regions of an appreciable area. Their origin is attributed to having homogeneous electromagnetic properties. An anomalous field may appear due the influence of flows of charged particles to an inhomogeneous structure of the geo- emitted by the Sun on the ionosphere of the electric section of an area being prospected, Earth, and therefore, they depend on the i. e. of the combination of geological bodies solar activity. and seams, each of which has particular 3: Artificial permanent electric fields prodimensions and specific electromagnetic duced in the Earth by means of earthed cables connected to a d. c. voltage source. parameters. In electric prospecting, the measured field 4. Artificial variable harmonic electromagparameters are the amplitudes and phase netic fields formed by various electric genshifts of the intensities of electric and mag- erators producing a voltage that varies harnetic fiel~. The principal electric properties monically in time. (parameters) of rocks are the specific electric With the use of an alternating current, a resistance, dielectric constant, magnetic per- field can be excited by an inductive (meability, electrochemical activity, and po- less) method. For this, a loop of a number of wire coils, usually of a square shape with the larizability. Depending on the problems to be solved, size from 10 m to 1000 m, is laid on the all methods of electric prospecting can be Earth's surface and connected to an a. c. divided into three groups: (I) profiling, which generator. 5. Transient electric and electromagnetic is used for the examination of inhomogeneous geoelectric sections represented by fields excited by quick switching of rectanclosely folded strata and electromagnetically gular d. c. pulses into the feed line. In any method of electric prospecting, the inhomogeneous inclusions; (2) probing, which is employed for the investigation of set of instruments contains electric generators

14.6.

Geodetic

Control

of Geophysical

and other supply sources, measuring and recording instruments, earthing electrodes or non-earthed contours for the galvanic or inductive field excitation, earthing electrodes and antenna rods for measuring the electric field components or frames and loops for measuring the magnetic components, and auxiliary equipment. 14.6.4. Seismic Prospecting Seismic prospecting for minerals is a geophysical method based on studying the propagation of elastic waves excited by explosions or other sources. Since rocks have different density and are characterized by different velocities of the propagation of elastic waves in them, reflected and refracted waves can appear at the boundaries between the rock strata and, besides, elastic waves of a different kind can form in inhomogeneous media. The records of these waves provide information on the structure of the region being studied. Seismic prospecting is based on the analysis of the kinematics and dynamics of waves. The seismic.methods of prospecting consist essentially in the excitation of elastic waves and detection of the induced soil oscillations which are transformed into electric pulses; these pulses are amplified and recorded on seismograms and magnetograms. These are processed in order to separate various kinds of seismic waves and determine the time of their propagation to a point with the known coordinates. Quantitative interpretation of the results of seismic prospecting gives the velocities of wave propagation, variations of their propagation along the depth and over an area, bedding depths of seismogeological boundaries, their dipping, extension, etc. Using additional geological characteristics, it is often possible to establish the geological nature of detected boundaries of geological bodies, i. e. to construct a seismogeological section. 22.

Prospecting

339

The principal methods of seismic prospecting are as follows: reflected wave method; refracted wave method, sometimes called refracted wave correlation method; transmitted wave method; method of common reflection point; method of vertical seismic profiling; etc. In practice, the reflected wave method is used most often, in particular for the dissection of sedimentary beds. It is the leading method for structural investigations and prospecting for petroleum, gas, and other minerals. The refracted wave method can provide information on the elastic wave velocities and the depth of beds composed of rocks with high elastic moduli and on the bedding depths of these rocks. The transmitted wave method is employed for detecting various inhomogeneities in rock beds. 14.6.5.

Magnetic

Prospecting

Magnetic prospecting is a geophysical method based on studying the spatial distribution of variations of the geomagnetic field which can appear due to different magnetization of rocks. The principal methods of magnetic prospecting are the aeromagnetic, hydromagnetic and ground magnetic surveys, underground and borehole observations, and the measurements of the magnetic properties of rock specimens. In any point on the Earth's surface, there exists a magnetic field which can be described by the total magnetic intensity vector T or its vertical (2) and horizontal (H) components. As a first approximation, the magnetic field of the Earth can be likened to the field of a uniformly magnetized sphere or dipole (To). In addition to this unifQrm field of the magnetized sphere, however, the magnetic field of the Earth also has the components of anomalous geomagnetic fields which are associated with continental (TJ, regional (T2), and local (T3) anomalies. In the practice of

340



magnetic prospecting, the normal magnetic field is usually taken as the field of a uniformly magnetized sphere (To) plus the continental anomaly (TJ. The normal geomagnetic field can be characterized by a normal gradient, i. e. a change in field intensity per kilometre. The deviations of the observed values of magnetic vectors from the normal field are regional or local anomalies depending on the area of their appearance. In magnetic prospecting, the measurements of the magnetic field may be either absolute or relative. In ground magnetic prospecting, however, relative vertical components of the geomagnetic field, A Z, are measured most often and, less frequently, relative values of the total vector, A 1;' i. e. increments of these characteristics relative to an initial (reference) point. Ground magnetic surveys can be done on scales from 1/50000 to 1/2000 and larger. With scales 1/50000, 1/25000 and 1/10000, geological magnetic surveys are carried out for mapping the territory being studied, as well as directly for searching iron-containing ores. Magnetic surveys on scales 1/10000, 1/5000 and 1/2000 are fulfilled for more detailed analysis of magnetic anomalies, detection of ore bodies and tectonic distortions, and for the estimation of the dimensions, shape and location of ore bodies. Ground magnetic surveys are carried out, as a rule,. on areas which are recognized prospective by the results of aeromagnetic surveys. Observation profiles are assigned across the strike of anomalies on aeromagnetic maps. Spacings between the profiles depend on the scale of surveys and can range from 500 m (1/50000) to 50 m (1/5000). Distances between the observation points on profiles should be 50-60 per cent smaller than the profile spacings. The connection of observation points can be done by instrumental (in prospecting work) or semi-instrumental methods. In the

latter case, however, the starts and ends of profiles and the centres of anomalies are connected instrumentally. 14.7.

Mine-Surveying in Geophysical

Work Prospecting

The principal object of the mine-surveying work in geophysical prospecting is to layout the set-up points for instruments and to determine their planimetric and height coordinates. A particular method of geodetic control in geophysical surveys is chosen mainly depending on the scale of geophysical work, provision of the geodetic basis, and physico-geographic conditions in the prospected region. The elevations and plan coordinates of points for geophysical measurements can be determined easily and efficiently by reference to topographic maps. If reliable maps are unavailable, the plan positions of points in regional geophysical surveys can be determined on aerial photographs. The elevations of these points are usually determined by barometric levelling. In geophysical field surveys on scales 1/50000 to 1/10000, point coordinates are most often determined by running main traverses (base lines) and laying out profiles between them. Theodolite traverses and level lines are then run along base lines and sometimes along profile lines. The topographic and geodetic control of geophysical prospecting includes the following steps: (a) the design positions of prospecting profiles or individual observation points are transferred into nature and fixed on the ground; in gravimetric and magnetometric prospecting, all observation points should be transferred into nature, and in seismic and electric prospecting, this involves all centres of excitation and reception of signals; the positions of profiles and individual points should be transferred onto the ground with

14.7. Mine-Surveying

Work in Geophysical Prospecting

the accuracy of planimetric connection; (b) observation points located on profiles and beyond them are connected, i. e. their plan coordinates and elevations are determined; this should be done for all points of geodetic observations; (c) the topographic basis for geophysical maps is formed; and (d) height differences around the gravimetric points are determined in order to take into the effect of a terrain relief on the measured values of a gravity force. In aerogeophysical prospecting, the plan connection of aerogeophysical routes is usually done by aerial photogrammetry. 14.7.1.

Mine-Surveying in Gravitational

Work Prospecting

The mine-surveying work in gravitational prospecting consists of the following operations: (a) the transfer of the design position of reference and ordinary gravimetric points into nature (laying-out of base lines, profiles, etc.); (b) fixation of the points by suitable marks;

341

(c) determination of the plan and elevation coordinates of observation points; (d) determination of relative height differencesaround observation points in order to take into the effect of a terrain relief; (e) provision of the geodetic basis for gravimetric maps; and (f) the technical control and estimation of the accuracy of the work performed. The planimetric connection of gravimetric prospecting points can be carried out by using topographic maps on scales corresponding to or larger than the scale of a gravimetric survey, aerophotogrammetric materials, instrumental geodetic methods, autometric topoconnectors, etc. For determining the elevations of gravimetric points, it is possible to use topographic maps on scales which ensure the required accuracy; geometric and trigonometric levelling; barometric levelling; materials of stereophotogrammetric surveys; and hydrostatic levelling. The permissible errors for determining the positions of the points of gravimetric observations are given in Table 14.6. In cases when the surface of observations

Table 14.6 Scale of gravimetric map

Interval, milligal

Root-mean square erros (m) of point position relal initial points

in elevation

in plan flat terrain

'1000000 '200000 '100000 150000

0.5 0.25

1/25000

0.25 0.20 0.20 0.10 0.05

mountainous terrain

1.0 0.50 0.50 0.25 0.50 0.20 0.10

flat terrain

::t200 ::t100 ::t80 ::t40 ::t40 ::t20 ::t20 ::t4 ::t4 ::t2

mountainous terrain

flat

terrain

mountainous terrain

:!: 5.0 :t 100

:!: 2.5

:t 100

:!: 1.2

:t 50

:!: 0.70

:t 50

:!: 0.35

:t 25

:!: 0.35

:t 25

:!: 0.25

:t5

:!: 0.20

:t5

:!: 0.10

:t2

:!: 0.05

:I: 3.0 :I: 1.8 :I: 1.6 :I: 0.9 :I: 0.9 :I: 0.45 :I: 0.25

:to.1

~



cartographic materials of an appropriate accuracy, which are not always available, especially for what is called the closer zone, i. e. the portion of the Earth's surface in the direct vicinity of a gravimetric point. In such cases, levelling of the surrounding terrain is carried out along radial rays (eight or sixteen). The radial distances from a gravimetric point to staffing points are usually taken equal to 1.2 m, 2 m, 6 m, 15 m, 35 m, 75 m or 150 m. 14.7.2. ~

"Z

Mine-Surveying Work in Electric Prospecting

The mine-surveying work in all kinds of electric prospecting is carried out mainly for the preparation and connection of obser~ vation points and detected anomalies on the Fig. 14.6 Terrain relief representedas combinaterrain and for laying-out and surveying of tion of elementaryseparations base lines and profiles. The principal requirements to the accudiffers substantially from a planar one deterracy of the mine-surveying work in electric mining the relief corrections which are introduced into the observed values of the gravity prospecting are given in Table 14.7. The mine-surveying work in various kinds force has certain specifics. With either positive or negative relief, the gravity force of electric prospecting has certain specifics. decreases, because of which the relief correction is always introduced with a positive sign. Corrections for the surrounding relief are calculated for individual annular concentric zones around a gravimetric point. Since the terrain relief in an annular zone may be variable, these zones are further subdivided into curvilinear prisms which are called elementary separations (Fig. 14.6). The real surface of each elementary separation is replaced by a horizontal plane whose elevation is equal to the mean elevation of the elementary separation relative to an observation point. The correction for the surrounding relief can be determined directly on a topographic map or by instrumental measurements. B For determining the relief corrections with the required accuracy, it is essential to have Fig. 14.7 Electric prospecting by probing --(

14.7. Mine-Surveying

Work in Geophysical Prospecting

343

Table 14.7 Method of electric prospecting

Map scale

Root-mean square errors of point position relative to initial points in

flat terrain

Natural field, induced polarization, transient, electroprofiling, isolines, etc.

Telluric currents, magnetotelluric profiling, and magnetotelluric probing Vertical electroprobing; dipole probing, partial electromagnetic probing Formation of electromagnetic field

in elevation

plan

mountainous terrain

1/5000

4

5

1/10000

8

10

5

1/25000

20

25

10

1/50000

40

50

1/50000

40

50

1/50

of reference

1/200000

160

200

level

depth,

more

than

5

10 but

not

15 m

Ditto

Ditto

Ditto

Specified

Ditto

Ditto

Ditto

1/50 of reference level depth

For instance, in the method of isolines, linear electrodes are laid on the ground at distances of 500-1500 m from one another and connected by insulated wires to the poles of a current source. The points of the same potential are found on the terrain by means of what is called a search circuit. The minesurveyor's task in this caseis to determine the positions of these points. In regional prospecting, the coordinates of these points are mainly determined by the materials of aerophotogrammetry and in detailed work, by instrumental methods. In induction, natural direct current and the like methods, the points for setting up instruments in regional prospecting are determined by reference to aerophotogrammetric materials and topographic maps and in detailed work, by measurements on a preliminarily laid-out square or rectangular network. In electric prospecting by probing methods, the object of mine-surveying is to determine the plan and elevation coordinates of a record point Q, which is required for the construction of a geoelectric section, the length of a feeding dipole AB, the area of a

receiving loop q, an active distance 001 and an angle 6 (Fig. 14.7). The length of the feeding dipole can be calculated by the coordinates of the feeding dipole AB centre 0 and the centre of a receiving circuit 01. The connection of points A, B, 0, and 01 is usually done by means of topographic maps or aerophotogrammetric materials. 14.7.3.

Mine-Surveying Work in Seismic Prospecting

In seismic prospecting by the reflected wave method, seismic profiles are laid out on the ground and connected in plan and vertically by instrumental methods. In the refracted wave correlation method, seismic profiles are connected instrumentally, and the explosion points located beyond the profiles are connected in plan. In seismic logging, it is required to determine the distances between the logged and explosion boreholes, height differences between them, and the direction angle from the logged boreholes onto explosion points. In spatial mass probing, the plan and elevation positions of probes and explo-

344



Table 14.8

Table 14.9

in

plan

in elevation

Scale of magnetic Root-mean square Relative error of surveying error of connection measured distance of initial point of between profile profile or base line points relative to initial points

1/50000 1/25000 1/10000 1/5000 1/2000 1/1000

sion points are determined, and the figure for the arrangement of seismographs is constructed. The accuracy requirements for the minesurveying work in seismic prospecting are given in Table 14.8. In seismic prospecting in seas at a small distance from the coast, observation points can be connected by means of a reflecting circle (index) by the method of resections onto the initial points on the coast. In such cases, profiles are ranged out by poles or buoys set up at intervals not more than 2-3 km in detailed surveys or 5-6 km in regional surveys. In cases when the seismic work is being carried out far from the coastal line, observation points are connected mainly by radiogeodetic methods. 14.7.4.

Mine-Surveying Work in Magnetic Prospecting

In ground magnetic surveys, the minesurveying work includes the transfer of the contours of a survey area, layout, connection and fixation of observation points, and the connection and fixation of detected anomalous zones, structures, etc. In ground magnetic prospecting, the methods of the preparation of observation points can be divided into three main types:

15 15 8

1/100 of interval between points on profile

8

(a) profile methods with a preliminarily laid-out observation network; (b) profile methods with the simultaneous semi-instrumental layout of an observation network; and (c) route methods with the observation points being read off from a topographic map or aerophotogram. In magnetic prospecting with a preliminarily laid-out observation network, the accuracy of the mine-surveying work should be as given in Table 14.9. Profile methods with the simultaneous semi-instrumental layout of an observation network are usually employed in the search work on a scale of 1/50000, 1/25000 or 1/10000 in woody territories; in that case, survey profiles can be ranged out by a magnetic azimuth, and distances along a profile can be measured by striding. Magnetic surveys are carried out, as a rule, along roads, forest cuttings, footpaths, rivers, etc., and the surveying net is connected visually to the orientation marks which are present both on the ground and on the map. The errors of the planimetric positions of points on a survey line should not exceed 1/4 of the spacing between the points, but not more than 250 m in any case.

14.8.

14.8.

Barometric

Levelling

Barometric Levelling of Geological Observation Objects

Table 14.10

:I: 0.35 :I: 0.5 :I: 1.0 :I: 2.5 :I: 5.0

Objects

345

Table 14.11

Barometric levelling has found rather wide use for the elevation control of geological surveys. It is mainly resorted to in caseswhen other levelling methods are insufficiently accurate or less efficient economically. The method is especially popular in gravitational prospecting. An essential advantage of barometric levelling is that it is applicable even when the points to be levelled are mutually invisible. The accuracy of barometric levelling depends on the instruments employed, kind of a terrain relief, and the techniques of levelling. Barometric levelling is based on a certain correlation between the elevation of a terrain and atmospheric pressure. As has been demonstrated by the practice of levelling, with properly organized work it is possible to measure elevations with an error less than 0.5 m. Depending on the accuracy of measurement of the elevations of geological observation points, the recommended accuracy in the measurements of atmospheric pressure is given in Table 14.10. Barometric levelling in geophysical surveys can be carried out by various methods, the choice of a particular method being dependent on the scope of work, available instruments, number of observations, and required

Root-mean square error of measured heights, m

of Observation

Time intervals between measurements of pressure and temperature of atmospheric air at barometric stations, min

Root-mean square error of measured heights, m

in flatland regions 0.35

10

0.5

10

1.0

15

2.5

20

5.0

30

at barometric

::!: 0.015

:t 0.010

::!: 0.020

:t 0.015

::!:0.05 ::!: 0.15

:t 0.03 :t 0.05

::!: 0.30

:t 0.10

mountain-

ous

regions

10 10 10 15 20

accuracy. In all methods, however, the measurements of air temperature at particular points and initial barometric stations are done at the same time with measuring the atmospheric pressure. Barometric stations should be located on open places with smooth shapes of the relief. It is not advisable to locate stations on sharp summits, in deep and narrow valleys, on the crests of cliffs, and (in summer time) near large water basins. Instruments for atmospheric pressure measurements should be placed at baromet-

Table 14.12 Root-mean Mean distance square error of observed of height dif- points from ference, m TBS *, kIn

Mean height difference of observed points relative to TBS *, m

without cor- with correction for sys- rection tematic error of air temperature measurement

Root-mean square error of measured atmospheric pressure, mb

at observation -~:-,.

in

0.4:> 0.70 0.90 2.0 .TBS

L.-() 2-9 2-13 10-25

-temporary

barometric

)U-IU 80-20 110-10 210-30 station.

14U-4j 245-55 320-45 680-180

346



Table 14.13 Time of traverse run, h

Root-mean square error of height difference, m

0.25

Mean length of tra. verse, km

1.0 2.0 4.0 1.0 2.0 4.0 1.0 2.0 4.0 1.0 2.0 4.0 6.0 8.0 2.0 4.0 6.0 8.0

0.45

0.70

0.90

2.0

Mean height difference of observed points relative to TBS, m without correction for systematic error of air temperature measurement

with correction

2.7

20-5

70-25

2.6

20-5

70-10

2-4

20-5

60-5

5-15

50-10

140-25

5-14

40-10

130-20

5-9

40-5

120-10

5-40

85-35

240-70

5-25

85-35

240-90

5-15 5-50

75-10 110-50

235-65 320-130

5-40

110-10

320-40

5-20

100-25

310-40

5-13

100-10

290-50

5-12

95-5

10-50

240-200

700-550

10-30

240-200

700-540

10-15

230-210

700-590

10-15

220-200

700-570

280-5

Table 14.14

Table 14.15

Root-mean Mean distMean height difference of square error ance between points relative to RBS * in of height dif- RBS *, km calculation, m ference, m

Root-mean square error of measured heights of points,

up to I

Permissible fInS error of comparison of mercury barometers at reference stations, mb

0.03

without cor- with correcrection for systion tematic error of air temperature measurement 1.2 2.0 3.5

50 50-130 150

* RBS -reference

barometric

180-50 250

station.

90 500-135 700

up 2.5

above 2.5

0.07

0.10

to

14.8.

Barometric

Levelling

of Observation

B

A

347

Objects

><

~

~

~

~

~

~

~

00 ,..; ;0 -

""' ai Ir) -

.,; O N

00 ~ +

V) ~ ""'

~ r-i -0 +

"' r-

11-

:=:

~

N tO -

<=!

N ...;

"' -

b

Fig. 14.8 Calculation of elevation of observed point by method with severalbarometricreference stations ric stations permanently for the entire period of station operation. Air temperatures are measured at barometric stations and measuring points by means of aspiration (sling) thermometers set up at a height roughly 2 m above the Earth's surface, with an accuracy to 0.5 degree C. Time intervals between the measurements at barometric stations and points depend on the error in elevation measurements at the points and can be determined according to Table 14.11. Barometric levelling can be carried out by one of the following methods. Barometric levelling by the methods of level lines can be performed with reference to one initial point.(closed level lines) or to two points (open lines). A temporary barometric station is arranged at the initial point of a closed level line. With an open level line, one temporary station is placed at the initial point and another, in any point of the line. In the method of closed level lines, it is possible to work with one or two barometers. Barometric levelling by the method of closed level lines should"be done according to the requirements given in Table 14.12. Barometric levelling by the method of open level lines is carried out with the use of two sets of barometers. In this method, the deviations of observed points from the range

Q,. ~

-

c '0 ""

:=;

~ ~ ,9 ~ ~

.. <

+ N r.: ~

0 ~

N oci .q1-

0-

~ c

~ " ~ &

.& ~ ~ .9 ~ ~

9 '" <

0It"i +

...; \I') r--

~ ci +

~

~

...

~ 0

~ 0 +

8 N O

o 0 N O

+

~

""'

8 "' 0

-0

!1 ~. e :I:.

"'

"1

1

"!

-I/") I/")

~

r-

~

~

...; 0-

~ ~

.., <

~

u

"'"

, .: ~o ".e,," o~ '" ~ ..() ~.E:

"' .. "1:) .:8 .g.~ """" ~; ~

~ ..; .. :s " ~

.I;) o 'O~

.:

0.8 Z""

N

'0 ~ >,0 -0 .,...,

348



line of initial points should be not more than 0.2 of the distance between these points. The principal requirements to the field work by this method are given in Table 14.13. In barometric levelling by the method with several barometric reference stations, these stations are located so that all points of observation can be inside the figure formed by the stations (in most casesa triangle). In a particular case, barometric reference stations can be located on the range line. The permissible distances between the barometric reference stations should be as recommended in Table 14.14. In this method, it is possible to use meteorological stations or special temporary reference stations. All barometers used at the stations are standardized by determining their corrections relative to one of them which is taken as the standard instrument. The standardization of barometers should be carried out with an accuracy as specified in Table 14.15. The elevations of observed points are determined by the results of the measurements of air temperature and pressure at these points, which are done at the same time with air temperature and pressure measurements at the stations. The point elevations are calculated as weighted mean values, by considering the following circumstances. Let an observed point O be inside a reference .triangle ARC (Fig. 14.8). The elevation of the point O can be calculated by the formula: H = H~k1 + H~k2 + H~k3

where H~, H~, and H~ are the preliminary elevations of the point observed and k1, k2, and k3 are the weight coefficients which depend on the position of the point and can be found by the formulae: k1 = 11/Ll, k2 = 12/L2, k3 = 13/L3 where 11= Oa, 12= Ob, 13= Oc, L1 = Aa, L2 = Bb, and L3 = Cc. The elevation of the observed point is calculated by a scheme given in Table 14.16. The elevations, H, of reference stations are recorded in column 4. The distances, I, from the observed point to the side connecting two other barometric stations are written as numerators in column 5 and the distances, L, from a barometric station to the same side through the point being observed, as denominators in the same column. Columns 7, 8, 9, and 10 contain data from the field books. The difference in atmospheric pressure, l\P , between the barometric station and the point observed is calculated in column 11. Column 12 contains the values of barometric stages. The values given in columns 11 and 12 are then multiplied to give the height difference between the barometric station and the point observed (column 13). The preliminary values of elevations found by algebraic summation of the elevations of barometric stations and elevation differences are written in column 14. Finally, column 15 gives the elevation of the 'point observed, which is obtained by summing the products of preliminary elevations and the c9rresponding coefficients.

Chapter

Mine-Surveying in Water

15.1.

Fifteen

Work for Mineral Extraction Areas of Seas and Oceans

General

One of the novel trends in mining industry is the exploitation of mineral resources of the Ocean bottom. Our knowledge of the Ocean is still insufficient for large-scale mining of its minerals, but it can be already stated quite definitely that the mineral reserves in the shelf and deep-sea zones of the Ocean are enormous and can be estimated approximately by the following figures: 4 x 1015t of aluminium, 100 x 109t of cobalt, 300 x 109t of nickel, 350 x 109t of copper, 42 x 109t of manganese,120 x 106t of zirconium, 80 x 106t of molybdenum, etc. In addition, almost all elements of the Periodic Table are present in the Ocean in the dissolved state. The sea medium has certain specific features which can influence the organization and accuracy of the mine-surveying work. The principal among them is the dynamics of water masses.The level surface of the Ocean is subject to periodic, non-periodic and secular variations. Periodic variations mainly include tidal oscillations. Non-periodic variations may be of geodyllamic or geothermal origin, i. e. they may be caused by earthquakes, underwater volcanic eruptions, tectonic disturbances in the Earth's crust, water surges, occasional sharp changes of atmospheric precipitation, changes of atmospheric pressure, etc. For estimating the dynamic conditions of the level surface of the Ocean, of prime importance are the tidal phenomena which may depend substantially on the geographic latitude, depth of sea, and the shape of a coastal line. The highest water level at

tides is called high water, the lowest level at ebbs is low water, and the medium level is what is called mean water. In open sea, the tidal variations of the water level are equal to roughly 1 m; near coasts, especially at the head of narrow bays, the difference between high and low water may attain a few tens of metres. The surface of seas and oceans to a depth up to 60 m can be disturbed substantially by winds which often create waves up to 12-13 m high. The effect of wind disturbance is especially detrimental for the accuracy of minesurveying observations, since prospecting and mining work in seasare carried out now and will be done in the nearest future only in the shelf zone where the effect of wind waves is quite strong. Water waves can be characterized by the length, height, velocity, period, front, and steepness. The length A of waves is the horizontal distance between the crests (or troughs) of adjacent waves; height h is the vertical distance from the trough to the crest of a wave; velocity v is the distance covered by a wave crest in unit time; wave period Tis the time interval during which two wave crests successivelythrough a given point; wave front is a line perpendicular to the direction of wave motion; and steepnessis the height-to-length ratio of a wave. As a wave approaches the coastal line, its profile changes substantially. The top portion of the wave slope facing the coast becomes steeper, i. e. the wave profile becomes asymmetrical. The asymmetry of waves is notice-

350


Work

able at depths roughly twice the wave height. At the coast, wave crests tip over and form feathers, or breakers. As the wind velocity decreases,water waves attenuate slowly, the rate of attenuation being proportional to the wave length. The waviness of the sea surface that remains after winds have ceased to blow is called swell, or aftertossing. 15.2. Brief Data on Geomorphology of Ocean Bottom Relief By modern concepts, the ocean bottom has four structural zones (Fig. 15.1). I. The first is the submerged margin I, which includes the shelf la, continental slope Ib, and continental base Ic. The submerged margin is regarded geologically as the flooded portion of the continental plateau which is characterized by relatively calm tectonic conditions and markedly prevailing slow vertical deformations of the surface. The shelf is essentially a shallow-water portion of the submerged margin, which extends from the coastal line to a sharp bend of the bottom surface, usually at a depth of 130-140 m. The part of a shelf to a depth of 30-50 m is called shoal. The continental slope is a relatively steep

in Water

Areas of Oceans

portion of the bottom at the external edge of the shelf. Its width is rather small and usually measures from 15 km to 30 km. Inclination angles are equal to 3-6° on the average, ranging from lO to around 45°. The surface of the continental slope is often furrowed by U-shaped valleys called submarine canyons. Submarine canyons may have a length from a few tens to a few hundreds of kilometres and penetrate to depths of 3-4 km. The continental slope changes to what is called the continental base, a slightly inclined undulating plain at depths of 2-4 km. 2. The transition zone II is an intermediate zone between the submerged margin I of the continent and the ocean bottom (floor) III. This zone has the basin of marginal sea at the side of the continental base and island arcs lIb and deep-sea troughs IIc, at the side of the ocean. The deep-sea troughs form the boundary between the continent and ocean, so that one of their slopes is represented by the continental crust and the other by the oceanic crust. 3. The ocean floor III is represented by the oceanic type of the Earth's crust and lies at depths of 2500-6000 m. It mostly has a hilly relief of the accumulative type with large oceanic troughs and uplifts.

Fig. 15.1 Profile of ocean bottom: l-submerged margin; la-shelf; lb-continental slope; lc-contin~ntal base; ll-transition zone; lla-pits of marginal seas; llb-island arcs; IIc-deep-sea troughs; III -ocean bottolD; lV -mid-ocean ridges

15.4.

Geological

Prospecting

4. Mid-ocean ridges are essentially mountainous formations of a width of 500-2000 kID. A depression, or rift valley, usually runs along the axial line of a ridge. At both sides of the rift valley, there are rift crests with individual summits 7000-8000 m high above the foot of a mid-ocean ridge. Earthquake centres (foci) are confined to rift crests. 15.3.

Characteristics of Some Solid

Minerals

and

Mining

351

of sands and a high concentration of useful components in them (up to 90% of non-native ones). As a rule, band-shaped shelf placers have discontinuities at capes and in river estuaries. Placers in the continental slope are usually located at distances from 500 m to 15 km from the coastal line and have a length of a few tens of kilometres and width, .a few hundreds of metres. The mechanism of transfer of heavier minerals forming a submarine placer is determined by the same processes as the transfer of the mass of sediments forming the bottom topography.

At present, over loo countries are carrying out geological prospecting in the water area of seasand oceans, and enormous reserves of minerals have already been discovered (Fig. 15.2). 15.4. Mine-Surveying Service Submarine deposits of minerals are conof Geological Prospecting ventionally classified by the following groups: and Mining in Water Areas metal-bearing concretions and red clays; primary deposits; and submarine sedimentaIn prospecting for submarine deposits, the ry deposits, mainly shelf placers and mine-surveying service has the following metal-bearing silts. objects: (a) the collection and examination of geoAt present, shelf deposits attract the main detic, hydrographic and meteorological interest, in particular, placer deposits formed due to the dynamic activity of seas and the documents available for a given water area; (b) the provision of the planimetric and chemical processes occurring in sea water. By the time of origin, submarine placers elevation survey control for the coastal part can be classed into buried (concealed), conof land and alloted water area; (c) the complementary surveys of the bottinental, and young (present-day). Buried placers formed on overlapping of ancient tom relief and prospecting workings; (d) the control of the positions of prosplacer deposits by younger sediments at changes of the sea level and displacement of pecting and mining workings in the water the coastal line. Continental buried deposits area upon their transfer into nature; (e) the compilation of the graphical are formed due to sinking of the coastal documentation of the alloted water area, surface of land below the sea level. All buried submarine placers, as a rule, are not subject which should reflect the bottom relief of a basin, the shape, dimensions and geological to hydrodynamic actions and lithodynamic changes. Present-day placers are more easily characteristics of a deposit, and the characaccessible for exploitation than other types, teristics of enclosing rocks; (f) surveying of underwater workings; since they are not covered by sediments. (g) the calculation of the mineral reserves; Present-day placers mostly have the shape of and bands extended along the coastal line. (h) the analysis of the lithodynamic chanDelta placers have an irregular shape in ges of the bottom relief. plan and variable characteristics. Shelf plaIn the construction of underwater worcers can be characterized by a very thin bed

352 Ch. 15. Mine-Surveying

Work

in Water

Areas of Oceans

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15.5.

Marine

Mine-Surveying

kings and the exploitation of deposits, the tasks of the mine-surveying service are as follows: (a) survey work for the construction of engineering structures in the water area (wharfs, pulp pipelines, hydro-engineering objects, etc.); (b) the development of measures for the protection of structures and environment against harmful effects of underwater workings; (c) the transfer of the geometrical elements of designed structures and objects into nature., (d) the control of assembling of plants, hydro-engineering objects, etc.; (e) the assignment of directions to stripping and preparatory mining workings; (1) servicing and control of the dynamics of stripping and mining work; (g) the complementation of mine-surveying plans, sections and graphical documentation with the results of the surveys of mining workings and waste dumps; (h) the compilation of mining-geometricaf graphs for more accurate determination of the shape of a deposit, quality of a mineral, properties of enclosing rocks, and the distribution of useful components; (i) the control of the variations in lithodynamic processesduring the exploitation of deposits and the prediction of changes in the depth and contours of underwater workings; and 0) the calculation of the dynamics of mineral reserves, output, losses and dilution of minerals. Mine-surveying measurements in the water area should provide data on the dimensions, shape and structure of submarine deposits, which are then represented in graphical documents. The mine-surveying work in water areas consists mainly in profiling of the sea bottom and underwate:r workings.

23-1270

15.5.

Reference

Nets

353

Marine Mine-Surveying Reference Nets

Marine mine-surveying reference nets are developed for making various surveys associated with prospecting and mining of the bottom of seas and oceans (Fig. 15.3). Depending on the distance from the coast, they can be divided into off-shore nets which are formed in the zone of geometric visibility from the coastal line and open-sea nets, i. e. those beyond the geometric visibility. Off-shore surveying nets are developed from geodetic nets on the shore land and

354


Work

in Water

(c)

Ibl

1a)

Areas of Oceans

12

(d)

(e)

Fig. 15.4 Benchmarks for marine mine-surveyingnets:(a) pole-type;(b) pile-type;(c) wooden frame; (d) metallicframe;(e)buoyant; 1- bottom of seaor basin;2 ~ water line; 3 ~ earth embankment;4- tube or rod; 5- benchmark centre;6- end fastening(plug);7~ concretefilling; 8- instrumentalplatform enclosure; 9-navigation signal; 10-bench mark platform or pontoon; 11-boundary of compacted layer; 12-concrete filling; 13-concrete base; 14-counterweights; 15-buoy rope; 16-anchors; 17-bottom centre those in the open sea, from the points of a polygonometric method is mostly employed marine mine-surveying net, in particular for deposits extended along the coastal line. from a local net connected to the geodetic The root-mean square error of determireference net on the land. nation of the direction angles of sides in Marine mine-surveying nets can be const- marine mine-surveying nets should not exructed by the methods of triangulation, trilaceed I'. For the plan positions of the points of teration and polygonometry. Reference nets a net, the rms error should be not more than for deposits located near the shore can be 0.2 mm on the scale of a plan. constructed by the methods of intersections, The elevation control for the surveying combined intersections or resections. The work in the near-shore water area is provided

15.6.

Special

Mine-Surveying

by levelling points. The absolute elevation marks of survey points on the shore are determined by geometric or trigonometric levelling and of those in the water area, mostly by trigonometric levelling. The rms error in the determination of heights of the points of marine (off-shore) nets relative to initial (control) bench marks should not exceed 0.02 m and the rms error of height difference between two adjacent points, should be not more than 0.05 m. When the water area is covered by firm ice, it is more preferable to use geometric levelling. The points of marine reference nets are fixed by means of special bench marks (beacons) which may be of the pole-type (Fig. l5.4a), pile-type (Fig. l5.4b), with a wooden or metallic frame (Fig. l5.4c and d), or buoyant (Fig. 15.4e) with automatic correction or recording of their deviations from the centre. Marine bench marks should be set up before the beginning of stormy seasons, and each should be provided with a navigation signal. If a marine mine-surveying net is developed on ice, its points can be marked by metal rods qr wooden poles frozen into the ice. Polygonometric traverses should be run so that the mean arithmetic error of the final point of a traverse line of any shape is not higher than the value calculated by the formula:

Work

in Water

Areas

355

nometric traverse; L is the length of the closing line of a traverse; mp is the rms error of angle measurement; n is the number of sides in a traverse; and D is the distance from the centre of gravity of a traverse to each turning point. The best time for observations and measurements is when the temperature of water surface is close to that of air, since this minimizes the effect of refraction on measured results. 15.6.

Special Mine-Surveying Work in Water Areas

In the general case, all kinds of the minesurveying work carried out on submarine deposits can be divided into special and routine. In special mine-surveying work, mine surVeyors together with geologists determine the geological and hydrogeological characteristics of deposits, geomorphological and lithodynamic specifics, hydraulic conditions in the water area, etc. The main object of special work is, however, to analyse the lithodynamic processes responsible for the variability of a given relief and to determine the principal parameters of the deposit and underwater workings. Surveys for mapping of a deposit should be carried out both in the period of detailed prospecting and during exploitation. It is principally important to decide on the frequency of repeated observations which should be such that the variations of relief that may occur between the surveys can be commensurable with the accuracy of surveying. The frequency of observations is usually determined experimentally. Special mine-surveying work also includes the formation and development of planimetric and elevation control (for off-shore and open-sea mine-surveying nets), establishment of level-gauging stations, navigation marks, etc.

356

15.7.


Work

in Water

Areas of Oceans

Routine Mine-Surveying Work in Water Areas

The main objects of the routine mine-surveying work are to provide the basis and control for geological prospecting and the basis for the mining work. The basis for geological prospecting in water areas is done by preliminary investigations which consist in observations on the hydrologic conditions of the sea and the lithodynamic processesin loose sediments on the bottom. These observations include large-scale surveys of the bottom relief and the determination of the planimetric and height coordinates of prospecting boreholes, contours of ditches and trenches, points of geological sampling, and the corner (final) points of traverses in mine-surveying and geophysical profiling. In the period of underwater mining work, mine-surveying service makes the surveys of underwater workings and represents them on the plans of the mining work and compiles profiles and sections. The results of surveys make it possible to calculate the volumes of extracted rock and determine the places of mineral losses and sources of mineral dilution. The set of mining graphical documentation includes the plans of the submarine mining work on scales 1/1000 or 1/2000, lithological sections along prospecting lines, and the profiles of ~arlier exploring and mining workings in the most typical directions. The contours of a deposit and design boundaries of underwater workings are transferred into nature and marked by means of stakes, beacons or buoys (Fig. 15.5) set up in the sea at intervals of 100-200 m. During prospecting and mining of a deposit, surveys are carried out in order to obtain the plan coordinates and depths of the points of the bottom relief and underwater workings. In practice, these measurements are usually made simultaneously. In the general case, the surveys of planimetric coor-

dinates and depth measurements are planned so as to attain the required accuracy and minimize the number of traverses which may have different directions depending on the pattern of the bottom relief and the purpose of surveying (Fig. 15.6). The survey method with parallel traverses is used most often (Fig. 15.6a). Traverses should be directed in the sense of the highest ruggedness of the bottom relief; for workings, they should be oriented perpendicular to their axis. Depth measurements can be made by zig-zag (Fig. 15.6b and c) or radial traverses (Fig. 15.6d). Zig-zag traverses are used when it is essential to reveal sharp bends of the relief, such as in hollows, valleys, ranges, etc. Radial traverses are run in cases when they can represent a relief without noticeable distortions (which is possible since radial traverses diverge from the coast or control points, i. e. distances between them increase with moving farther into the sea). Radial traverses are used, for instance, for surveying of capes, off-shore bars, islands, and extended and weakly dissected surfaces of the bottom relief. The root-mean square error of locating the bottom relief points in mine surveys should be not more than 1.5 mm on the scale of a

15.7.

Routine

Mine-Surveying

Work

in Water

Areas

(a:

(c)

Id)

,~~ -I

,

\--

~

~ Fig. 15.6 Typical schemes of traversing in bottom relief surveying: (a) with parallel traverses; (b) with zig-zag extension traverses; (c) zig-zag traversing with control extension traverses; (d) radial traversing with additional transverse extension traverses

358


Work

in Water

Areas of Oceans

base line and the line of sight on a vessel);Dl and D2 are the distances from the base points to a vessel; and mp is the instrumental rms error of angle measurement. The plan position of a moving target is determined by the method of linear intersection with the use of optical or radio range finders and with reference to two or three initial points. Optical range finders are employed in cases when linear intersections are made to relatively shortJ distances (up to 2 km and less frequently, up to 4-5 km). When the objects of marine surveys are removed from the coast to distances more than 3 km, use is made of high-precision radiogeodetic and radionavigation systems which can determine the positions of points in the sea with the rms error around 1 m. 15.9.

where v is the vessel velocity, m/s; D is the distance from an observer to the measured point, m;
mmt =

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b2

2 .4 p Sill

(

.2 mIl Sill

A + Sill .2 1'1

)

A 1'2

'1

+~)J D~ where b is the length of a base; 'Y is the angle at the measured point; 1:11and 1:12are the angles at the base points (angles between the

Depth

Measurements

The measurements of the depths of bottom points relative to the sea level can be made by sounding poles, sounding leads,echo sounders, photometric and stereophotogrammetric methods. At present, echo sweeps and bottom-scanning sonars (asdics) are being employed widely. A sounding pole is a metal or wooden round pole up to 5 cm in diameter and up to 8 m long, which has 5-cm or 10-cm graduations. Depths can be measured by sounding poles with an accuracy to 2-3 cm. A hand sounding lead consists of a hemp or metal rope with a lead or cast-iron weight around 5 kg in mass tied to its end. The rope is graduated in metres and decimetres by the marks of different colour. Hand leads can measure depths up to 50 m with a relative accuracy of I/lOO to 1/200. A mechanical lead (sounding machine) has a winch with a counting mechanism, rope, and weight up to loo kg in mass. The accuracy of depth measurements by sounding machines depends on the degree of rope sagging which is determined by the size and shape of the weight,

15.9.

Depth

Measurements

359

Fig. 15.7 Operation oflaser-acousticsystemin bottom profiling: Ah3-height of lasersight abovebench mark; R,,-elevation of point (benchmark) in adopteld system;h -depth of measuredpoint on echogram; ho-reading of nth stageof photodetector;hi -readil Ig of laser beam on vertical staff water flow velocity, variations of water velocity along the depth, and the length of a rope. At present, depth measurements are most often made by using echo sounders whose operating principle is based on the propagation of ultrasonic pulses emitted by an ultrasonic source and reception of pulses reflected from the sea bottom. The oscillations of floating vesselsin rough sea reduce substantially the accuracy of depth measurements by echo sounders. This effect is largely eliminated in laser-acoustic systems which have come into use in recent time. A laser-acoustic system (Fig. 15.7) is a combination of a laser and echo sounder and consists of a laser sight 1 with a scanning attachment 2, vertical staff 3 with a photodetector, acoustic system 4, electric pulse generator, amplifier, and a recorder. The laser sight sends a beam 0-01 which defines a reference plane and enters the photo-detector on the staff. The received

pulse is transmitted to a pulse delay generator which fonns a delayed pulse and then sends a starting pulse to the generator. The latter produces an electric pulse to excite the acoustic system which transfonns electric pulses into acoustic signals. Upon reflection from the sea bottom, acoustic signals are transfonned back into electric pulses. These are sent to the recorder which makes a record of the sea bottom depths and the elevation marks of the sea level. The measured values of depths are reduced to a particular level of sea surface which is called the hydrographic datum, or datum level. For seaswith small amplitudes of level oscillations (height of tide up to 0.5 m), the mean water level of many-years observations is taken as the datum level. For seas with substantial level oscillations, the lowest level surface of the sea is taken as the datum level. In surveys in water areas, depths are measured relative to a conventional (phantom) horizon which is called the datum and is

360


Work

somewhat lower than the horizon of the lowest level. This is done in order that calculated levels may be always positive. A level-gauge station, or simply gauge, is made in the form of a level-measuring pole which is fastened to a pile, wharf or another stationary structure. Level-gauge poles are mostly made of cast iron and have inserted porcelain pieces forming 2-cm graduations. Enamel-painted metal poles are also in use. Depth measurements are also carried out for studying the lithodynamic processes, in particular, the intensity and amount of wash-out (erosion) or, on the contrary, the accumulation of drifted sediments on the bottom and in underwater workings. The thickness of an active layer of sediments is established by measuring the maximum depth in fixed points in the periods of rough sea, which can be done by the method of a 'movable disc' or by successive measurements between the periods of rough sea. The former method is employed at depths up to 3 m and consists essentially in that the disc is let to slide down a metal rod fixed in the bottom, after which the depth of disc sinking is determined on the staff that is connected with the disc and protrudes from water. If the bottom ground is washed out, the disc sinks deeper and this is detected by the changed position of the staff. Staff readings can be done instrumentally from the on-shore or off-shore points of a reference net. . The method of successivemeasurements is not as accurate as the former, but is less laborious. Measurements are carried out strictly on the same profiles, and the thickness of an active layer is determined by differences between successivemeasurements. 15.10.

Calculation of Extracted

of

Volumes Rock

The volumes of rock extracted in subma. rine mining can be calculated by the follow.

in Water

Areas of Oceans

ing methods: (I) by the results of surveying; (2) by measuring the volumes of extracted rock shipped in ore carriers or contained in on-shore stores; (3) by the readings of flow meters and consistometers mounted on pulp pipelines. Volume calculation by results of surveys. This method can be recommended for cases when the contours of mining workings are not changed substantially during the period of measurements. The calculation of the volume of the extracted mineral on the basis of the results of surveys can be made most easily by the method of horizontal sections. The volume of a working is determined by the formula: v = hm8m where hm is the mean depth of a working, m and 8m is the mean area of a working, m2. The mean area is found as the half-sum of the upper and lower areas: 8m = (8u + 8,)/2 and the mean depth: hm = ~h.I/ n where ~hi is the sum of measured depths within the boundaries of a working floor, m and n is the number of measurements. In practice, the mean extractive capacity of a mineral is usually determined as the difference of the mean elevation marks of the surface of a submarine deposit (within the boundaries of the upper crests of slopes) and of the bottom or as the difference of the mean depths of a working floor and the mean depths of the initial surface of the sea bottom. Calculation of volumes in vessels and onshore stores. In this method, the mine surveyor has to make the following operations: (a) measuring the geometrical parameters of a vessel or store; (b) determining the coefficient of filling of a capacity with loose rock mass; (c) calculating the volumes of loose rock in

15.10.

Calculation

of Volumes

of Extracted

Rock

361

(I) making an additional survey of submarine workings in order to determine the Rock Rock Loosening Loosening mineral reserves left in the ground and the factor factor amount of losses and dilution. -The most difficult step is the determination Sand 1.01-1.02 Loam 1.15-1.30 River gravel 1.03-1.04 Clays 1.30-1.45 of a loosening factor, but this can be taken Gravel 1.07-1.18 Shingle 1.40-1.60 from Table 15.2. Coarse- and Hard rocks 1.45-1.65 Determination of volumes of rock mass mediumtransported through pulp pipelines. In this grain sand I. 14-1.28 Frozen flood case, the volumes of rock mass are determiplain dePebbles, ned in of the flow rates of pulp crushed posits in transported through pipelines and measured stone I. 23-1.30 river valby means of flow-meters and consistometers. Sandv ]nam 1.1 07-1.18 leys and Hydraulic-type flow-meters are used to estuaries 1;20-1.17 - measure the flow rate of hydraulic mixture a waste dump or vesselby the formula for the (pulp) sucked in by a dredge. The density of a volumes of regular geometrical bodies (a pulp is determined by the pressure gradient appearing in the pulp in a vertical pipeline cone, pyramid, cylinder, cube, etc.); (d) determining the loosening factor of the owing to the settlement of heavier fractions. extracted rock by considering the physical Automatic recorders have been developed state and quality (moisture content, granu- which record instantaneous and summarized lometric composition, etc.), time of storage, data on the throughput capacity of a pumand the amount of settling; ping station and dredge, pulp density, and (e) recalculating the volume of loose rock actual time of operation. The error of volume to that of rock in the rock massif, using the measurements by flow-meters is not more than 3 per cent. loosening factor; Table 15.2

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