This paper discussed the influences on soil resistance of a pile group caused by different soil properties and failure criterions. Nonlinear static analyses were performed using 3-dimensional finite element method. The major conclusions of this paper can be summarized as follows: 1) Under the Mohr-Coulomb failure criterion, the strength of sand differs between triaxial compression and triaxial tensile. The difference determines the subgrade reaction of piles. 2) In the case of sandy soil,

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... de reaction concentrates on front piles in a pile group. While in the case of cohesive soil, the concentration on front piles is softened by side piles.