Macro and micro-behaviors of anisotropy granular soils using 3D DEM simulation

Anisotropy has a significant effect on the strength and deformation characteristics of granular sand. In order to study the macro- and micro-behaviors of anisotropic sand, a series of numerical triaxial tests are performed on seven specimens with different bedding angles using the three-dimensional discrete element method (DEM). The approximate ellipse-shaped particles are generated using the command of clump, and a 3D rolling resistance model is implemented to simulate the local rolling resistance between particles. Good agreement is achieved between the present DEM simulation results and previously published experimental results. The relationship between deviator stress and axial strain changes from strain softening to strain hardening with the increase in bedding angel. The specimens with smaller inclination angels are more dilative and easier to reach the critical state. The combined invariants representing the relative orientation of particle orientation fabric tensor and stress tensor can approach nearly to -1. Their fabric anisotropies of particle orientation increase first and then decrease. However, for the specimens with higher bedding angels, the critical state cannot be reached even when the axial strain reaches 50% and the combined invariants are much larger than -1. Their fabric anisotropies first drop and then continuously increase. For the contact normal based fabric tensor, the principal axe rotates instantly toward the principal axe of the stress tensor, and the evolution of fabric anisotropy is similar to that of deviatoric stress against the axial strain.