Thursday, December 12, 2013

Cast in-Situ Piles

Cast in-situ piles are the piles which are cast at the workplace or site itself. They are further classified into two categories:
(1) Driven cast-in-situ
(2) Bored cast in-situ

In driven cast-in-situ construction first we have to drive a steel casing into the soil, and then the reinforcement cage is put in this steel case and, concreting is done with a large slump value of about 10 cm.
The steel case is lifted upwards as the concreting is progressed in the upper direction.
chisel for drilling
This method is not preferred much because this requires a lot of hammering and displacement of the soil and thus effects the surrounding soil strata.

This method has reported the tension failure of the piles which are freshly constructed in the nearby area. Generally in the city areas this method is avoided because it disturbs the surrounding structures.

Bored cast-in-situ method of construction of piles is different in the manner that this do not use the steel casing but a pile hole is bored first and then the reinforcement cage is lowered in it and after wards concreting is done.

So hammering is not required here but, we will need the drilling tools like chisel along with the Bentonite slurry which is used to stabilize the soil of the bore walls and also to mix the drilled soil with it and take it out along with it.

The bentonite to be used should conform to the following requirements:
Density -  -- >  1.03 - 1.10 > 1.12    ---> Mud density balance method
Viscosity --->  30-60      ---->  Marsh cone method
Shear strength(10 min gel) ---- >  1.4 to 10.0 N.m2  ---> Shear meter method
pH --->  9.0 - 11.5  ---> pH indicator or paper strip.
Liquid Limit ---> 450%  ----> Casa-grande apparatus

Bentonite can be used with the chisel and bailer or,
Bentonite slurry can be used with the help of a powerful pump and the method is known as the continuous mud circulation method.