Numerical evaluation of pile group effect of a composite group

Pile group effects of a composite pile group that consists of a group of subgroups are investigated based on a series of static pushover analysis with the help of the nonlinear three-dimensional finite element method (FEM). The numerical result suggests that there is an interaction between subgroups as well as an interaction within each subgroup; the former interaction effect is very similar to the latter if the distance between subgroups is normalized with respect to an equivalent pile diameter of each subgroup. A simplified method to estimate pile group effects of a composite pile group is then proposed in which the interaction effects within and between the subgroups are both accounted for using the same P-multiplier approach commonly employed for a pile group. The P-multipliers estimated by the proposed method show a fairly good agreement with those estimated from the FEM analyses.