Vane Shear Test.docx j6r4l

Vane Shear Test OBJECTIVE To find shear strength of a given soil specimen. NEED AND SCOPE The structural strength of soil is basically a problem of shear strength. Vane shear test is a useful method of measuring the shear strength of clay. It is a cheaper and quicker method. The test can also be conducted in the laboratory. The laboratory vane shear test for the measurement of shear strength of cohesive soils, is useful for soils of low shear strength (less than 0.3 kg/cm2) for which triaxial or unconfined tests can not be performed. The test gives the undrained strength of the soil. The undisturbed and remoulded strength obtained are useful for evaluating the sensitivity of soil. PLANNING AND ORGANIZATION EQUIPMENT 1.Vane shear apparatus. 2.Specimen. 3.Specimen container. 4.Callipers. EXPERIMENTAL PROCEDURE 1.Prepare two or three specimens of the soil sample of dimensions of at least 37.5 mm diameter and 75 mm length in specimen.(L/D ratio 2 or 3). 2.Mount the specimen container with the specimen on the base of the vane shear apparatus. If the specimen container is closed at one end, it should be provided with a hole of about 1 mm diameter at the bottom. 3.Gently lower the shear vanes into the specimen to their full length without disturbing the soil specimen. The top of the vanes should be atleast 10 mm below the top of the specimen. Note the readings of the angle of twist. 4.Rotate the vanes at an uniform rate say 0.1o/s by suitable operating the torque application handle until the specimen fails. 5.Note the final reading of the angle of twist. 6.Find the value of blade height in cm.

7.Find the value of blade width in cm. Standard Penetration test (SPT) CONCEPT The Standard Penetration test (SPT) is a common in situ testing method used to determine the geotechnical engineering properties of subsurface soils. It is a simple and inexpensive test to estimate the relative density of soils and approximate shear strength parameters. DESCRIPTION AND PROCEDURE Standard Penetration Test, SPT, involves driving a standard thick-walled sample tube into the ground at the bottom of a borehole by blows from a slide hammer with standard weight and falling distance. The sample tube is driven 150 mm into the ground and then the number of blows needed for the tube to penetrate each 150 mm (6 in) up to a depth of 450 mm (18 in) is recorded. The sum of the number of blows required for the second and third 6 in. of penetration is reported as SPT blowcount value, commonly termed "standard penetration resistance" or the "N-value". The N-value provides an indication of the relative density of the subsurface soil, and it is used in empirical geotechnical correlation to estimate the approximate shear strength properties of the soils.

MACKINTOSH PENETRATION TEST / JKR PROBE TEST

The Mackintosh Probe development was based on the principles stated by Hvorslev (1948) for drive rods for sounding and sampling and recommended methods for static and dynamic sounding by European Group Subcommittee (1968). The probe consists of a cased screwed onto the lower end of the rod. The rods are of 16mm diameter HY steel each of length 120 cm. The rods are connected to each other by 25 mm outer diameter couplings. These couplings provide the lateral to the rods so as to prevent buckling during driving. Driving is performed with a small hammer of 5 kg in weight and falling vertically through a fixed height of 30 cm along a guide rod. The total number of blows required for the pointer to penetrate a distance of 30 cm is recorded and used as a measure of the consistency of cohesive soil and the packing of granular soil. The relationship between Mackintosh Probe and Safe Pressure is as follows: P = (2860 + P = Refer Chart

550

(R

-

40) 1/2)

x

0.04788 kN/m2 for blows < 40

for

blows

>

40

Where, P= safe pressure R = Mackintosh Probe Penetration resistance in blows/0.3m

(kN/m2)

cone penetration test (T) CONCEPT The cone penetration test (T) is a common in situ testing method used to determine the geotechnical engineering properties of soils and assessing subsurface stratigraphy. The test is also called, Dutch Cone test. Due to its simplicity and efficiency, the cone penetration test is one of the most commonly accepted and used in-situ testing methods in geotechnical investigation worldwide. DESCRIPTION AND PROCEDURE The cone penetration test (T) is a common in situ testing method used to determine the geotechnical engineering properties of soils and assessing subsurface stratigraphy. The testing apparatus consists of an instrumented still cone having a tip facing down, with an usual apex angle of 60° and cross-section area of 1000 mm2. The code is attached to a internal still rode than can run inside a outer hollow rod, which itself is attached to a sleeve. In the more elaborate T instruments, the cone and the sleeve (attached to the outer rod) can move separately. The Cone penetration test can be carried out from the ground surface with a need for a borehole. The test is carried out by first pushing the cone into the ground at a standard velocity of 1 to 2 cm/s while keeping the sleeve stationary. For any depth, the resistance of the cone, called cone penetration resistance q_c , is recorded using the force probes provided for this purpose in the cone. Then the cone and the sleeve and moved and penetrated together into the soil and the combined cone and sleeve resistance, indicated by q_t , is recorded at any depth using tension load cells embedded in the sleeve. This procedure is repeated and the measurements are made at regular depth intervals during penetration. In addition to the stress on the tip and the sleeve friction, the typical T probe measures as well the porewater pressure. Some equiped T probles are also able to measures shear wave velocity and temperature. The cone penetration resistance values can be then correlated to shear strength parameters using proposed empirical curves. There are also some design methods associated with T results which directly use the T results to estimate the settlement is soils under a given pressure.

PIEZOCONE The piezocone test (TU) is a cone penetration test (T) with additional measurement of the porewater pressure at one or more locations (U1, U2 and U3) on the penetrometer surface (Figure 8).

Cone penetration testing, with porewater pressure measurements,

gives a more reliable determination of stratification and soil type than a standard T. In addition, TU provides a better basis for interpreting the results in of mechanical soil properties. Mechanical properties to be evaluated are:  shear strength parameters 

deformation and consolidation characteristics.

The results from a TU can be used, directly, for the design of piled foundations in clay.