Hey Vijay,

It’s often economical to use pile foundation where sub soil has poor or uncertain bearing capacity or where there is likely appreciable ground movement as is with black cotton soil or sinkable clay or where the foundation is deeper than 2 meters.
The design and size of pile may be decided according to bearing capacity of soil, nature of soil, load coming on it and spacing of piles. It also depends on the mix of cement concrete and steel used in piles.
The actual size, depth and diameter of pile can be designed after obtaining field data and calculation of load coming on it. The ratio of cement concrete mix may be obtained from laboratory which depends on the quality of material used in the mix.
For obtaining size of piles and other details contact structural engineer giving all field data and concerned drawings.

Thanks.