Initiation of granular surface flows in a narrow channel

TL;DR

This study experimentally examines how a granular pile in a narrow channel transitions from stability to flow when inclined above the angle of repose, analyzing flow development and velocity profiles against a visco-plastic model.

Contribution

It provides detailed experimental insights into the initiation and evolution of granular surface flows in confined geometries, validating a visco-plastic model with new velocity profile data.

Findings

Flow accelerates then stabilizes into a steady regime

Flow thickness increases during initiation

Velocity profiles match visco-plastic model predictions

Abstract

We experimentally investigate how a long granular pile confined in a narrow channel destabilizes when it is inclined above the angle of repose. A uniform flow then develops, which is localized at the free surface. It first accelerates before reaching a steady uniform regime. During this process, an apparent erosion is observed and the thickness of the flowing layer increases. We precisely study the evolution of the vertical velocity profile in this transient regime. The measurements are compared with the prediction of a visco-plastic model [P. Jop, Y. Forterre and O. Pouliquen, Nature 441, 727 (2006)]