Rheology, force transmission, and shear instabilities in frictional granular media from biaxial numerical tests using the contact dynamics method

Abstract

[1] By means of the contact dynamics discrete element method, we investigate the quasistatic behavior of granular media composed of rigid frictional particles. Eluding specific modeling of the contact rheology, this method is suitable for numerical simulation of the plastic deformations of granular materials. We studied the macroscopic stress-strain and volume-change behavior, as well as force transmission and shear instabilities, in a two-dimensional biaxial geometry for dense samples composed of 5000 rigid disks. The peak and residual strengths and shear bands were analyzed by varying the confining pressure and the coefficient of friction between particles. The results are consistent with well-known features of the plasticity of noncohesive granular media. The mechanical behavior is rigid-plastic governed by a Mohr-Coulomb yield criterion and showing strain hardening and softening. Conjugated shear bands characterize plastic failure. The volumetric strain is globally dilatant with considerable expansion observed along shear bands. The macroscopic coefficient of friction, determined from peak and residual strengths, increases nonlinearly and saturates to a constant value as a function of contact friction. The strong force chains are mostly parallel to the major principal stress axis, yet deviations are observed near the shear bands. These chains are often composed of particles that are larger than the average. The deviatoric stress shows small fluctuations often in the form of rapid falls that are correlated with tiny contractional events. This behavior is interpreted in terms of the propagation of dynamic shear instabilities along the shear bands, in close analogy with stick-slip behavior.Citation: Taboada, A., K.-J. Chang, F. Radjaï, and F. Bouchette (2005), Rheology, force transmission, and shear instabilities in frictional granular media from biaxial numerical tests using the contact dynamics method,

Bonded-cell model for particle fracture

“…In CD, an iterative algorithm based on nonlinear Gauss-Seidel iterations is used to determine the contact forces and particle velocities simultaneously at all potential contacts. The CD method has been extensively employed for the simulation of granular materials in 2D and 3D [55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72].…”

From discrete to continuous numerical identification of a geomaterial with an internal length

“…We propose to limit these phenomena by using a cylindrical container and a low confinement pressure range. This pressurization step is carried out via a special procedure [13] which applies precomputed forces directed toward the cylinder axis on sample particles located in a thin peripheral layer. To be completely free of edge effects, the identification procedure is limited to a spherical volume included in the sample.…”

Rock‐and‐soil avalanches: Theory and simulation

“…For cohesionless particles, the CD method is based on the implicit time integration of the equations of motion, the nonsmooth formulation of impenetrability and Coulomb friction, and the dissipation of energy by means of a restitution coefficient. An introduction to the CD method is given by Taboada et al [2005b] and Pöschel and Schwager [2005].…”

“…However, simulations of shear tests on granular samples performed at low strain rates may give some insights on failure and fragmentation mechanisms in granular flows [e.g., Taboada et al, 2005b]. During shearing, the principal stresses show fluctuations and instabilities that result from reorganizations in the contact force network.…”