Influence of Rotations on the Critical State of Soil Mechanics

TL;DR

This study investigates how hindering grain rotations affects the critical state in soil mechanics, revealing that increased rotational difficulty leads to higher shear strength and altered micro-mechanical properties.

Contribution

It introduces a particle-level friction coefficient to quantify rotational hindrance and demonstrates its impact on the critical state through molecular dynamics simulations.

Findings

Larger rotational hindrance increases final shear strength.

Micro-mechanical variables like anisotropy are affected by rotational thresholds.

Rotations play a key role in soil critical behavior.

Abstract

The ability of grains to rotate can play a crucial role on the collective behavior of granular media. It has been observed in computer simulations that imposing a torque at the contacts modifies the force chains, making support chains less important. In this work we investigate the effect of a gradual hindering of the grains rotations on the so-called critical state of soil mechanics. The critical state is an asymptotic state independent of the initial solid fraction where deformations occur at a constant shear strength and compactness. We quantify the difficulty to rotate by a friction coefficient at the level of particles, acting like a threshold. We explore the effect of this particle-level friction coefficient on the critical state by means of molecular dynamics simulations of a simple shear test on a poly-disperse sphere packing. We found that the larger the difficulty to rotate, the larger the final shear strength of the sample. Other micro-mechanical variables, like the structural anisotropy and the distribution of forces, are also influenced by the threshold. These results reveal the key role of rotations on the critical behavior of soils and suggest the inclusion of rotational variables into their constitutive equations.