Gravity Governs Shear Localization in Confined Dense Granular Flows

TL;DR

This study reveals how gravity influences shear localization in confined dense granular flows, showing universal scaling laws and providing insights for predicting granular flow behavior in different gravitational settings.

Contribution

It introduces a variational analysis combining experiments to elucidate gravity's role in shear localization, revealing universal scaling laws applicable across environments.

Findings

Flow profile is gravity-independent with a free top surface.

Increased gravity shifts shear zones from buried to surface-intersecting.

Flow profiles follow universal scaling laws when scaled by gravity, pressure, and layer thickness.

Abstract

Prediction of flow profiles of slowly sheared granular materials is a major geophysical and industrial challenge. Understanding the role of gravity is particularly important for future planetary exploration in varying gravitational environments. Using the principle of minimization of energy dissipation, and combining experiments and variational analysis, we disentangle the contributions of the gravitational acceleration and confining pressure on shear strain localization induced by moving fault boundaries at the bottom of a granular layer. The flow profile is independent of the gravity for geometries with a free top surface. However, under a confining pressure or if the sheared layer withstands the weight of the upper layers, increasing gravity promotes the transition from closed shear zones buried in the bulk to open ones that intersect the top surface. We show that the center position and width of the shear zone and the axial angular velocity at the top surface follow universal scaling laws when properly scaled by the gravity, applied pressure, and layer thickness. Our finding that the flow profiles lie on a universal master curve opens the possibility to predict the quasistatic shear flow of granular materials in extraterrestrial environments.