Exploring macro- and micro-scale responses of sand in direct shear tests by numerical simulations using non-circular particles

The main objective of this study is to explore the macro- and micro-scale responses of sand in the direct shear tests by discrete element simulation. Non-circular particle element is self-developed in particle flow code in 2-dimension (PFC2D). The stress-dilatancy relationship of numerical samples is compared with that of real sand. The evolution of shear band is studied in relation with the variation of particle displacement and rotation. The effect of non-coaxiality between the directions of principal stress and principal strain increment is examined. Special attention is focused on the evolution of stress-induced fabric anisotropy during the shear loading. It is found that the discrete element simulation has a good ability to reproduce the stress-dilatancy relationship and non-coaxiality effect of real sand. The formation of shear band is strongly dependent on the distributions of particle displacement and rotation. A strong correlation between the shear strength and the evolution of normal contact force is evident in the simulation results. Coincidence between the orientation of normal contact force anisotropy and the direction of the major principal stress has been observed during all stages of shear loading.