Experimental Investigation of Plastic Deformations Before Granular Avalanche

TL;DR

This study experimentally investigates the progressive plastic deformations in granular materials before avalanches, revealing localized micro-failures and their dependence on various conditions, enhancing understanding of granular plasticity.

Contribution

It provides the first detailed spatially resolved analysis of micro-failures and their role in the plastic behavior leading up to granular avalanches.

Findings

Micro-failures occur periodically at high tilt angles.

Localized deformations decrease with depth.

Micro-failures depend on grain type, humidity, and packing.

Abstract

We present an experimental study of the deformation inside a granular material that is progressively tilted. We investigate the deformation before the avalanche with a spatially resolved Diffusive Wave Spectroscopy setup. At the beginning of the inclination process, we first observe localized and isolated events in the bulk, with a density which decreases with the depth. As the angle of inclination increases, series of micro-failures occur periodically in the bulk, and finally a granular avalanche takes place. The micro-failures are observed only when the tilt angles are larger than a threshold angle much smaller than the granular avalanche angle. We have characterized the density of reorganizations and the localization of micro-failures. We have also explored the effect of the nature of the grains, the relative humidity conditions and the packing fraction of the sample. We discuss those observations in the framework of the plasticity of granular matter. Micro-failures may then be viewed as the result of the accumulation of numerous plastic events.