Abstract: The behaviors of the sands near the interface between saturated loose sand and a sheet pile in an undrained state under high frequency cyclic shear are simulated by using the particle flow code in 2-dimension (PFC2D).The parameters which influence the volume strain and porosity of loose saturated sand near the interface are investigated.Besides,the variation of pore water pressure and the particle motion traces near the interface are studied.Numerical simulation results show that shear-contraction appears in saturated loose sand during high frequency cyclic shear,and the shear-contraction is obvious when the values of the parameters,including the particle friction coefficient,particle stiffness,shear amplitude and shear frequency,are smaller.However,it is also obvious when the values of the parameters,including boundary confining pressure and frictional coefficient,are larger.The porosity of the sand near the interface decreases firstly,then increases a little,and then decreases until reaching a steady value.The pore water pressure near the interface increases cumulatively.Sand particles near the interface have large displacements,and the value of the displacement become larger and larger with the reduction of the distance between the interface and sand particles.