Axial Resistance of Nondisplacement Pile Groups in Sand

When subjected to axial loading, the response of a pile in a pile group is different from that of an isolated single pile, all other factors being the same. Three-dimensional finite-element analyses were performed to study the response to vertical loads of nondisplacement pile groups in sand. The analyses were done with an advanced bounding-surface-plasticity constitutive model. The mechanical response of soil elements at various locations between the group piles was thoroughly investigated to reveal the underlying pile-soil-pile interaction mechanisms. Pile group efficiency was found to be a function of the pile head settlement, number of piles in the group, pile-to-pile spacing, and relative density of the sand. The effect of cap-soil contact on the pile group resistance development was also studied. For small pile groups, the group efficiency is close to or greater than 1 at settlement levels likely to be of interest in design.