Q. Method of construction of a bored cast-in-situ concrete pile?

Ans. - Bored cast-in-situ concrete pile - A guide casing of 3 to 4 m length is provided on top of the bore hole and is driven with the help of a bailer. Further boring below this casing is carried out by chiselling and the side walls are kept stable by circulating bentonite slurry inside the bore hole. The Bentonite clay used in the operation should conform to provisions made in IS : 2911 -Part -1, section -2. After reaching the founding level, the chisel is removed, the bore hole flushed and the reinforcement cage lowered into the hole and held in position by tack welding it to the support bars at the top of the casing.

After this the concreting is carried out by using a "tremie" .The concreting is continued till a good quality concrete is seen at the top of the bore hole. The concrete used is a high slump mix (not leaner than M 20 grade ). Cast-in-situ piles in which the steel shell is left in the ground ensures the quality of concrete and offers corrosion protection in soils containing chlorides and sulphates.