In this study, 3D finite element analysis is carried out to investigate the behavior of single pile and a group of free-head piles subjected to lateral soil movements. The mobilization mechanism of resistance from passive pile groups is discussed from the standpoint of the arching effect. Lateral pressure distributions along piles that vary with pile spacing, interface roughness and relative displacement between the pile and soil are determined. Computational simulations are adopted to consider the effect of pile spacing and the variation of internal friction angle on the lateral response of a pile in a row in cohesionless soil. It is observed that the loads acting on the piles increase with increasing of the pile spacing due to soil arching which is not effective after larger spacing than 8d. It is also revealed that the acting loads arrive at the maximum value and remain constant when the relative displacement exceeds 1.2 fold pile diameter. (C) 2009 Elsevier B.V. All rights reserved.