Quasi-Static Rheology of Granular Media Using the Static DEM

Abstract

In contrast to the conventional discrete element method (DEM), no dynamic or damping variables are needed in the static DEM. This study aims at investigating the potential of the static DEM in modeling the quasi-static deformation of stiff granular materials, in which the conventional DEM performs poorly. To represent flexible boundary conditions in the static DEM, the variational formulation for the bonded particle approach is developed, and these formulations are implemented with two-dimensional numerical examples. The boundary conditions are of great importance in numerical simulations. Their effects on the mechanical behavior of granular media are studied at the particle scale. The results show that the force transmission from the boundary to the specimen is more efficient under the rigid boundary condition than under the flexible boundary condition. Finally, the quasi-static behavior of perfectly rigid granular media is investigated with biaxial numerical tests. The peak and residual strengths and strain localization are analyzed by varying the confining stresses and the rolling resistance coefficient. The numerical results are consistent with the common experimental observations in terms of macroscopic stress-strain response, volume-change behavior, strain localization, and force transmission. The macroscopic mechanical response of perfectly rigid particles is a hardening-softening plastic behavior governed by a Mohr-Coulomb yield function. It is also shown that the width of the shear band decreases significantly when the rolling resistance coefficient increases.