Three-dimensional deformable discrete element method is an appropriate numerical method for studying mechanical behavior of discontinues geo-material. The ability of automatic contact detection and discretization of particle and structure by finite difference grids

makes it had inherent advantages in simulation discrete-continuum coupling problem. The deformable discrete element method is employed to study the mechanical behavior of soil-structure interaction problem

in which the coarse-grained soil is modeled by random simulation technique. The mechanical behavior of interface between soil-structure is compared under direct shear and simple shear conditions. The numerical simulation results are investigated from macroscopic and mesoscopic levels

respectively. The results show that the numerical simulation can reflect the mechanical behavior of soil-structure interface; the curves of shear stress-relative shear displacement have a good agreement with the experimental results; the interface roughness has a great impact on the strength and deformation properties

due to the disturbance of particle induced by shear. The shear stress-relative shear displacement relationships of simple shear and direct shear are both hyperbolic. The initial stiffness of simple shear is smaller than that of direct shear; and the shear strength of two are similar.