The influence of inter-particle friction and the intermediate stress ratio on soil response under generalised stress conditions

Abstract

Previous research studies have used either physical experiments or discrete element method (DEM) simulations to explore, independently, the influence of the coefficient of inter-particle friction () and the intermediate stress ratio (b) on the behaviour of granular materials. DEM simulations and experiments using photoelasticity have shown that when an anisotropic stress condition is applied to a granular material, strong force chains or columns of contacting particles transmitting relatively large forces, form parallel to the major principal stress orientation. The combined effects of friction and the intermediate stress ratio upon the resistance of these strong force chains to collapse (buckling failure) are considered here using data from an extensive set of DEM simulations including triaxial and true triaxial compression tests. For all tests both  and b affected the macroand micro-scale response, however the mechanisms whereby the force chain stability was improved differ. While friction clearly enhances the inherent stability of the strong force chains, the intermediate stress ratio affects the contact density and distribution of orthogonal contacts that provide lateral support to the force chains.

Hydrostatic and Shear Behavior of Frictionless Granular Assemblies under Different Deformation Conditions

“…The asymptote is referred to as the deviatoric steady state or the macroscopic friction, where represents the mobilized friction at each step along the loading path. For lower volume fractions, higher maximum are reached and the deviatoric stress ratio increases faster, meaning a higher ratio, where is the octahedral shear modulus as defined by Barreto and O Sullivan, 2012. This is opposite to what is expected for the shear modulus itself, being proportional to the volume fraction.…”

Macro–micro responses of crushable granular materials in simulated true triaxial tests

“…To date, considerable studies using DEM have been conducted to investigate the shear behavior of granular materials under a complex stress path [10][11][12][13]. In these studies, DEM simulations of polydisperse spherical particle systems were performed under constant mean stress (or constant minor principal stress) with varying b values.…”

Discrete-element method analysis of the state parameter

“…There is also a scarcity of large-strain laboratory test data for 3D general loading conditions; this limits the ability to develop and to apply these models to field applications where the stress state is not axisymmetric. Prior studies simulating true-triaxial element tests (Thornton 2000;Ng 2004;Barreto & O'Sullivan 2012; have shown that DEM can replicate the failure envelopes proposed for real sands. Thus, if a DEM model can be shown to capture the sensitivity of the material response to ψ that one would expect for a real sand, there is then potential to use DEM to advance critical state-based constitutive models for sand.…”