Analysis of Downdrag on Pile Groups by the Finite Element Method

The downdrag on friction and endbearing pile groups was investigated, based on a numerical analysis. The emphasis was on quantifying the reduction of downdrag on pile groups, with a flexible pile cap, due to group effect. The case of a single pile and, subsequently, the response of groups were analyzed by developing interaction factors obtained from a three-dimensional nonlinear finite element study. Based on a limited parametric study, it is shown that the downdrag on piles in a group is much less than the downdrag on a single pile and is highly influenced by the group spacing, total number of piles, and the relative position of the piles in a group. In light of all these influencing parameters, a simple method is recommended for square groups of 9-25 piles with spacing-to-diameter ratios of 2.5 and 5.0 for downdrag loads.