DEM and experimental study of bi-directional simple shear

Stress–strain responses of granular material under bi-directional simple shear are comprehensively studied experimentally and numerically. The variable direction dynamic cyclic simple shear apparatus is used to test glass beads under various loading paths, and the DEM is used to reproduce experimental results. These two methods are complementary to each other. The glass beads are subject to the first shearing until a specified shear strain is reached, followed by the second shearing until the failure of samples, and the two shears are at various angles. The experimental results are in good agreement with the numerical results. Both experimental and numerical studies indicate that the development of shear stresses is dependent on the angle between the two shears in the early stage, and they approach the same ultimate values at the failure. The lateral stress, principal stress and non-coaxiality are also studied in the DEM simulation. While the lateral stress and principal stress are dependent on the angle, the orientations of principal stresses and plastic strain rate almost reach the same value at the failure. The contact force network and material fabric are also investigated to provide insight into the micro-scale responses and macro–micro relations regarding bi-directional simple shear.