Cost comparison of pile foundation with reference to other foundation

1. In general the pile require foundation is likely to be more expansive than spread footings or mat.
2. Weak soils with heavy column loads require either rafts or piles. Rafts, in general are more economical than piles. But, when rafts become very large, piles have to be used for restricting both cost and settlement.
3. When piles and rafts are both equal in cost, then piles are preferable to rafts, as the settlement for piles is considerably less than that of rafts. Thus, pile foundations have to be used when raft foundations are not suitable on grounds of economy or settlement considerations.
4. Generally up to 3 to 4 floors (storeys), provision of raft foundation works out to be economical when a medium bearing/moderate bearing soil is available upto a depth of 2 to 3m. However for structure having more than 4 storeys and a hard strata is available only 10m depth below ground level, then adoption of pile foundation is the best in addition to be economical.
5. The key to economy in the pile foundations is to keep the area of pile cap in plan to the minimum, for which high capacity piles should be used. 
6. Capacity of a pile is increased by increasing either the diameter or depth of a pile, pile spacing (equal to three times the diameter) will increase and this will lead to a large pile cap, which will result in increased cost. So, pile depth should be increased to get high capacity piles. Thus, economy requires the use of a few high capacity deep piles under a column rather than a large number of low capacity shallow piles.