Particle-scale origins of shear strength in granular media

TL;DR

This paper investigates how particle properties influence the microstructural anisotropy and shear strength of granular media, highlighting the roles of connectivity, force chains, and anisotropy in shear resistance.

Contribution

It introduces a geometrical model linking particle connectivity and contact anisotropy to shear strength, considering steric effects and force anisotropy in granular materials.

Findings

Connectivity and anisotropy are limited by steric exclusions.

Weak forces play a key role in force chain stability.

Particle shape and friction influence shear strength.

Abstract

The shear strength of cohesionless granular materials is generally attributed to the compactness or anisotropy of their microstructure. An open issue is how such compact or anisotropic microstructures, and thus the shear strength, depend on the particle properties. We first recall the role of fabric and force anisotropies with respect to the critical-state shear stress. Then, a model of accessible geometrical states in terms of particle connectivity and contact anisotropy is presented. This model incorporates in a simple way the fact that, due to steric exclusions, the highest levels of connectivity and anisotropy cannot be reached simultaneously, a property that affects seriously the shear strength. We also analyze the force anisotropy in the light of the specific role of weak forces in sustaining strong force chains and thus the main mechanism that underlies anisotropic force patterns. Finally, we briefly discuss the effect of interparticle friction, particle shape, size polydispersity and adhesion.