ABSTRACT
The effect of all of the foregoing points will be to increase the plan area and/or embedment depth of a shallow foundation. These effects may also occur simultaneously such that the foundation would be too expensive or difficult to construct. In these circumstances, deep foundations may offer a more efficient and less costly design. Where shallow foundations are wide compared to their depth, deep foundations are elements which are much smaller in plan but extend to greater depth within the ground. The most common type of deep foundation is the pile, which is a column of concrete, steel or timber installed within the ground (Figure 9.1). Piles may be circular or square in section, but will always have an (outside) diameter (D0) or width (Bp) that is very much smaller than their length (Lp), i.e. Lp >> D0. A pier or caisson is another type of deep foundation which has a much larger diameter compared to its length, i.e. Lp > D0, but which can be analysed in the same way as a pile. Caissons are often used as foundations for offshore structures.
