Anisotropic characteristics of granular materials under simple shear

QIAN Jian-gu(钱建固)^{1, 2}, YOU Zi-pei(由子沛)^{1, 2}, HUANG Mao-song(黄茂松)^{1, 2}

(1. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education (Tongji University),
Shanghai 200092, China;
2. Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China)

Abstract:The discrete element method was used to investigate the microscopic characteristics of granular materials under simple shear loading conditions. A series of simple tests on photo-elastic materials were used as a benchmark. With respect to the original experimental observations, average micro-variables such as the shear stress, shear strain and the volumetric dilatancy were extracted to illustrate the performance of the DEM simulation. The change of anisotropic density distributions of contact normals and contact forces was demonstrated during the course of simple shear. On the basis of microscopic characteristics, an analytical approach was further used to explore the macroscopic behaviors involving anisotropic shear strength and anisotropic stress-dilatancy. This results show that under simple shear loading, anisotropic shear strength arises primarily due to the difference between principal directions of the stress and the fabric. In addition, non-coaxiality, referring to the difference between principal directions of the strain rate and the stress, generates less stress-dilatancy. In particular, the anisotropic hardening and anisotropic stress-dilatancy will reduce to the isotropic hardening and the classical Taylor’s stress-dilatancy under proportional loading.

Key words:simple shear; discrete element method; anisotropy; non-coaxiality