Evolution of shear zones in granular materials

TL;DR

This study investigates how shear zones evolve in granular materials with different shapes, revealing that particle shape significantly influences zone width, density, and reorientation during shear in split bottom shear cells.

Contribution

It provides new insights into the shape-dependent evolution of shear zones in granular flows through combined experimental and numerical analysis.

Findings

Zone width decreases initially with shear strain

Shape anisotropy increases the characteristic shear strain for zone narrowing

Final shear zone width is smaller for irregular and elongated particles

Abstract

The evolution of wide shear zones (or shear bands) was investigated experimentally and numerically for quasistatic dry granular flows in split bottom shear cells. We compare the behavior of materials consisting of beads, irregular grains (e.g. sand) and elongated particles. Shearing an initially random sample, the zone width was found to significantly decrease in the first stage of the process. The characteristic shear strain associated with this decrease is about unity and it is systematically increasing with shape anisotropy, i.e. when the grain shape changes from spherical to irregular (e.g. sand) and becomes elongated (pegs). The strongly decreasing tendency of the zone width is followed by a slight increase which is more pronounced for rod like particles than for grains with smaller shape anisotropy (beads or irregular particles). The evolution of the zone width is connected to shear induced density change and for nonspherical particles it also involves grain reorientation effects. The final zone width is significantly smaller for irregular grains than for spherical beads.