3-D DEM simulations of drained triaxial tests on inherently anisotropic granulates

A series of triaxial tests were simulated by the discrete element method (DEM) to study the effect of inherent anisotropy on the mechanical behaviours of granulates. In this study, clumps consisting of a collection of rigid spherical balls were used to simulate irregular-shaped particles, and the multi-layer under-compaction method was employed to prepare the anisotropic specimens with different initial density and fabric. The macroscopic responses including the strength characteristic, the volumetric response, the critical state and the stress-dilatancy relationship were carefully examined. In addition, two microscopic descriptors, the particle orientation (PO) fabric and contact normal (CN) fabric, were mainly monitored and investigated to shed light on the underlying micro-mechanics. The results show that comparing to the experimental results on natural sands, the typical macro-mechanical behaviours of anisotropic granulates can be successfully captured in the DEM simulations. Specimens with smaller inclination angle are more dilative. Nevertheless, the influence of the inherent anisotropy on the shear-dilatancy relation seems to be limited. The joint invariants N-P representing the relative orientation between the particle fabric direction and stress direction can be taken as an indicator of critical state. The rearrangement of the CN is more sensitive to the applied force than that of PO.