What is the difference between a pile foundation and an ordinary foundation?

Answer 1

Pile foundations are typically much deeper than they are wide. This means that their ability to resist loads is mainly derived from the vertical friction of the side of the pile against the soil (skin friction). However it should be noted that a number of closely spaced piles will act as a group and as such can also have significant resistance to loads by end bearing.

Regular foundations rely on the bearing pressure between the soil and the underside of the foundation, they are cheaper and more common. Piles will be used when greater forces are needed to be transferred to the ground over a smaller area, such as with high rise buildings and those in densely built up areas where land comes at a premium and ground movements will affect neighbouring buildings. A pile can be thought of as analagous to a tent peg whereas an ordinary foundation is like a flagstone.