Method Statement Tnb Substation 306e

METHOD STATEMENT FOR TNB SUB-STATION

1) Pile Foundation

 All piling works for the foundation will comply with the requirement as per the specifications for piling.  The pile points will be marked at specified locations, the hydraulic rotary drilling rig (or) RTC rig is aligned to the exact location and the verticality of the Kelly is checked.  The temporary casing if required is driven along with the advancement of pile boring. No permanent casing is envisaged. The verticality of the temporary casing is then checked by spirit level while lowering of bore and is recorded.  The process of lowering the casing and boring by auger is continued till the temporary liner reaches required level. The verticality and the lateral shift of the pile are checked at regular intervals. When the bore is intercepted with soft rock in the process of boring, the tool bit will be changed from soil auger to rock auger/barrel for further boring through soft rock. Once pile reaches the level as specified in drawing, the boring is stopped and the bore is cleaned by bucket and sounding is checked.  The pre-fabricated reinforcement cages in standard lengths will be cut for the required length taking into the bore depth, cut-off level, lap length etc. Reinforcement cages are then welded together into the bore. Cover blocks of suitable size will be tied to the reinforcement and lowered. Before lowering the reinforcement cage the lap length and welds will be checked and recorded.  Once the reinforcement cage is placed in position, tremmie pipes are lowered up to the toe level and the bore is flushed properly. Content coming out of the bore is checked for rock, sand and soil particles if any. Once the bore is clear, the same will be approved by the Engineer.  The concrete for pile of the required grade and slump as per mix-design will be produced at the batching plant and transported to site using transit mixers and placed by suitable method. Through tremmie pipe the concrete will be allowed to overflow to at least 1m above the cut off level. The tremmie pipes and temporary casing will be removed in stages as the concrete builds up in the pile. The tremmie will be inside concrete by minimum 1.5m at all the times till end of concrete.  The pile load test will be carried out at location specified by client.

2) Installation pile cap

 Once all the piles at a pier location are completed, the reconnaissance survey with the Engineer will be done and the pile cap layout will be marked on the ground to commence the excavation work for pile caps.  Open excavation of slope 1:1 with a bottom working space of 0.6 m maximum is considered. The excavation will be done using excavator up to 100 mm above the binding concrete level. The

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dressing will be done manually and the loose patches will be removed and compacted using a hand hammer. The sides of the excavated pits will be protected using shoring wherever required so as to prevent collapse and also to allow for the movement of traffic in the ading area. The pile heads will be chipped to the required level i.e. to the soffit level of the pile cap and the blinding concrete will be placed. Reinforcement from the pile will be bent to the required shape and the pile cap reinforcement will be placed and tied along with starter bars for the pier. The side forms / block work with solid blocks for the pile cap will be fixed and checked for the edge co-ordinates and levels. After approval of the engineer, concrete will be placed in position. In the mean time the starter concrete for the pier will be cast on the top of the pile cap, which will be used for casting the piers. The pile cap will be cured for 14 days. Backfilling of the pile cap will be done in layers and compacted using excavated materials/ fill material as required in specification.

3) Installation Slab & Beam Construction (cast-in-situ)

 Erect the slab formwork either using conventional scaffold framing and timber combination or using system formworks.  After the slab formwork is done, apply releasing agent using rollers for ease of striking. Meanwhile, the slab reinforcement bars can be brought into the slab formwork ready for installation.  Lay the main reinforcement bars of bottom layer of the slab spaced evenly according to design or drawings.  Tie the reinforcement bars at both ends to maintain the spacing.  Lay the distribution bars and tie them to the main reinforcement bars.  Install additional slab reinforcements if there’s any.  After completing the bottom layer of slab reinforcement, allow the M&E contractors to lay the concealed services.  Install bar chairs acting as spacers between top and bottom reinforcements.  Lay the top reinforcements with distribution bars fixed on first and the main reinforcements on the upper layer (transverse direction).  After completing the slab top reinforcements, clean and blow away the dust by using compressed air.

 Meantime, the surveyor must check the formwork level and install the markings for the concrete level.  After the formwork level measurements are done, furnish the copy from the surveyor and locate the area which varies from the correct level.  After the adjustment is done, do a routine formwork inspection to check the stability of the frames and runners.