Chapter 55: Pile-group design

Pile design often focuses on ultimate geotechnical capacity. When piles are located within a pile group, a wide range of additional factors need to be considered, including the deformation of the pile group and the structural forces induced in the piles and pile cap. Interaction between adjacent piles depends on several factors, including the direction of applied loads. When large horizontal loads are applied a complex range of interaction effects may need to be considered. Computer-based analytical methods are commonly used; nevertheless, it is important to use simplified methods of analysis both for preliminary design and to judge the reliability of output from computer-based methods. Pile-group deformation is usually more critical than group capacity, and, hence, the selection of appropriate deformation moduli is particularly important. Case history data and predictions from nonlinear modelling are compared with linear elastic methods. The delegation of design responsibility for pile-group design requires careful judgement and is also discussed.