Group shape effects on the lateral capacity of pile groups in undrained soil

In this paper, the lateral limiting pressure on rectangular pile groups in undrained soil is explored using two−dimensional finite element modelling. The primary aim of the study is to assess the influence of pile group shape effects on the soil limiting pressured offered by the deep ‘flow-around’ failure mechanism, and associated soil failure mechanisms, considering both a small (four piles) and large (36 piles) group. Additional parameters considered in the modelling include pile spacing and pile-soil interface roughness. The finite element results show that group shape has a significant influence on the behaviour of closely spaced pile groups. In particular, the number of piles parallel to the direction of loading is shown to dominate the lateral bearing capacity factor such that significant increases in capacity efficiency can be achieved by slight modifications to the group shape for a given number of piles. The load-sharing across the group, traditionally defined using p-multipliers, was also shown to be highly non-uniform and dependent on group size, pile soil roughness and group geometry in addition to the pile spacing. The finite element output is presented in the form of design charts for the determination of group p-multipliers whereas a library of existing design solutions is presented for the calculation of the overall group response