Pile Foundations - Uses.

Piles are generally used as a means of transferring loads down through unsuitable bearing strata either by skin friction and end bearing or end bearing only into a firm layer at greater depth (see Fig. 9.31).

There are many different types of piles including concrete – in situ and precast; steel; timber; stone. The cross-section of the pile and the installation method vary significantly.

In addition to transferring loads to greater depths below surface level the stone pile system (vibro-stabilization) can be used to upgrade the bearing capacity of the sub-strata (see Fig. 9.32).

The distribution of load through the sub-soil varies with the various types of pile and different installation methods.

Some piles are suitable for sandy soils, others for clay soils or end bearing into rock. The aim however is generally the same and that is to provide an economic means of support for the foundation and its loads. The various pile types and/or systems have advantages and disadvantages which make each pile more suitable and competitive for particular situations and soil conditions. There is perhaps a danger of the designer, having selected a competitive system on the first piling job, making the assumption that it is also the appropriate pile system to use on future contracts and ignoring the fact that the competitive tender probably related as much to the site and ground conditions as it did to anything else.

There is, therefore, a need for designers to understand the various types of pile, their best application, and possible limitations, etc., in order to provide good engineering solutions for design purposes. The following sections which describe the various types will assist the engineer in his choice of suitable pile systems and applications.

Fig. 9.31 Typical pile foundation.

Fig. 9.32 Stone pile (vibro).