Numerical study on behavior of super-long two-pile foundation in homogeneous soil

Based on the three-dimensional finite element method(3D FEM),the behavior of super-long two-pile foundation in homogeneous soil was investigated.During the course of establishing the finite element model,both the piles and soil were simulated using 8-node isoparametric elements in order to consider the co-action of the piles and soil,and a layer of thin element was placed along the side surface of the piles in order to consider the possible nonlinear deformation between the piles and soil.The relationship between stress and strain of concrete around the piles was simulated using a linear elastic model,that of the foundation soil was simulated using a nonlinear elastic model suggested by Duncan & Chang,and that of the special thin element was simulated by a special model suggested by Hohai University of China.The computed results indicated that the vertical stiffness of the piles in the super-long two-pile foundation increased with the increase of the distance between the two piles or the length of the piles,but the stiffness was always less than that of single super-long pile.The coefficient of two-pile foundation effect defined by the combination of critical tip resistance and side resistance of the piles was also investigated.The coefficient increased with the increase of the settlement at pile top or the distance between the two piles.But with the increase of the pile length,the coefficient first decreased and then increased or was almost invariant.