Downdrag Forces in Group of Piles

This paper describes a boundary element analysis for analyzing the behavior of a group of end‐bearing piles subjected to negative friction. It is found that group effects lead to a reduction in downdrag force in a pile, as compared with a single isolated pile, and that inner piles in a group develop less downdrag force than the outer piles. Among the factors influencing the distribution of downdrag force in the group are the number of piles, the relative stiffness of the piles, the distribution of soil modulus with depth, and the presence of pile‐soil slip. A significantly larger soil surface settlement is required to mobilize full pile‐soil slip along all piles in the group than along a single pile. When applied to a published field test, the theory shows reasonable agreement with the measured behavior.