Hydraulic rig/manually operable auger should be mobilized at the required location
Four reference points (making two lines perpendicular to each other) should be marked for checking centre of pile bore during boring of pile.
Initial boring of about 2.0 meters is to be done using cutting tool of desired diameter of pile
Then boring will be carried out according to the sub-soil investigation report of that location. It will be done using liner, bentonite or both.
The temporary guide casing, approximately 2.0 meter length with outside diameter equivalent to nominal diameter of the pile, may then lowered in the bore hole. In such a case dia of cutting tool will be little less, maximum 75 mm less than outside dia of casing for free movement in the casing pipe during operation.
Position / centerline of the guide casing pipe with reference to pile reference points already fixed around the pile location shall be checked to shift/adjust the casing pipe to ensure proceeding of drilling at exact pile location without any deviation.
Boring has to be done up to the founding strata as per drawings/ pre decided depth using intermittently bentonite slurry as per requirement. In case of requirement the bore hole is then supplied with bentonite slurry, from bentonite installation. Bentonite circulation channel will be made from bore hole to bentonite tank and fresh bentonite slurry will be pumped to bore hole through hose pipes. 24 hours prior to start of pile boring, ensure that bentonite is completely dispersed I the water and attains required density to stabilize the sides of bore hole during drilling. Bentonite slurry of specified quality should be circulated continuously during boring process.
Bentonite used to stabilize the sides of bore hole should be conforming to requirements as listed in inspection and test plan. Density of bentonite solution should be checked during boring operation to ensure that the density is about 1.05 g/cc to 1.10 g/cc, marsh cone viscosity 30 to 40 and pH value 9.5 to 12.
Bentonite slurry is pumped by high pressure reciprocating pumps/ vertical pump into the bore hole and the same is allowed to overflow the bore hole. The overflow slurry with bored mud/soil etc that comes out along with bentonite slurry is passed through channels and is collected in sediment tanks where sediments settle and bentonite can be re used. If necessary, the bentonite may be passed through the de sander tank to remove sand particles before it is re used.
Depth of pile shall be checked with sounding chain and exact depth shall be recorded in the pile report.
After boring upto required depth underreaming will be done using underreamer of desirable diameter. Completion of desired bulb cutting will be ascertained by (i) vertical movement of the handle and (ii) using L shaped rod of length enough to reach upto bulb location from approximately 2 feet above ground level and horizontal dimension equal to 0.5 of bulb dia minus pile dia.