Abstract: To study the internal particle motion and the structural change of the coarse-grained soil in direct shear tests, a two-dimensional discrete element numerical simulation method was used to analyze the horizontal motion characteristics of coarse-grained soil particles in the shear process from the microscopic point of view. The influence of the tangential bond strength of the simulated occlusion between particles on the cohesion and internal friction angle of the coarse-grained soil was analyzed. The results show that in the numerical direct shear test of the coarse-grained soil, the relative horizontal displacement of particles at different positions in the shear box is not the same. The coarse-grained soil particles with large relative horizontal displacement form an arctic shear band near the contact surface of the upper and lower shear boxes, and with the increase of the normal stress, the thickness of the arctic shear band also increases gradually. The tangential bond strength of the simulated inter-particle occlusion is positively correlated with the cohesion of coarse-grained soil, and there is no significant relationship with the internal friction angle.

Key words: Coarse-Grained Soil, Direct Shear Test, Discrete Element Method, PFC2D