To the program schedule considering all safety polices.
Location of piles will be set out, and it will be checked and verified by the consultant according to the approved shop drawing.
The bored pile to be cast from a suitably leveled platform with at least 20 cm thick road base bed, which elevation will be according to the pile cut off level and depth of ground water.
Procedure for construction of bored piles with temporary casing using Bentonite slurry system consists of three main stages, which are surveying, boring, reinforcing and casting.
For fixation of pile points standard reference points are used. At least two reference points is required for coordinate system and at least one reference point for standard level. Using precise survey instrument, like total station, coordinates of pile is fixed on ground with respect to standard coordinates. Generally these points are fixed on ground by inserting steel bars into ground at the concerned location. Before starting piling work coordinates are verified again to minimise location error.
Sequence of Piles:
Before starting piling work, piles are sequentially coded either by serial number or using grid codes as convenient for reference.
Steel reinforcement cages will be prepared according to approved drawing and materials. Length & number of main reinforcement and pitch of shear reinforcement (helical stirrups) will be checked and approved by consultant before placing.
A temporary short steel casing, known as guide casing, to be installed for guiding in boring of pile. It also supports top loose soil and prevents collapse of top layer due to machinery movement and vibration. Piles are normally drilled using hydraulic rotary rig with special tools (augers and buckets) to bore in different soil conditions.
Borehole should be filled with Bentonite slurry, which is prepared and stored at special plant; this slurry will maintain stability of borehole wall.
Density, viscosity and pH of bentonite will be tested daily.
Properties of Bentonite mix should be maintained daily as follows;
Viscosity: 40 to 90 sec.
PH value: 9 to 12
When founding level has been reached, steel-reinforcing cage will be lowered into the borehole. Concrete / plastic spacers will ensure the central location of the cage.
Concrete Placing: After getting approval for steel top level from consulting engineer, high slump concrete will then be poured using tremie pipe to displace the bentonite from bottom upward and pump back to bentonite storage tanks.
actual base bottom. On completion of pouring concrete, the temporary steel casing will be pulled out from the ground leaving the finished pile.
Concrete shall be cast above the cut-off level to avoid any contaminated concrete which may present at the top.
EQUIPMENT FOR PILING WORKS
For piling work following equipments are used:
Hydraulic piling rig.
Bentonite mixing plant.
Capacity of each equipment is depends on dimension of pile and site / soil condition.