On the dependence of the avalanche angle on the granular layer thickness

School of Engineering and Applied Sciences, Harvard University - 29 Oxford Street, Cambridge, MA 02138, USA and Janelia Farm, HHMI - 19700 Helix Drive, Ashburn, VA 20147, USA

Corresponding author: wyartm@janelia.hhmi.edu

Received: 31 July 2008
Accepted: 16 December 2008

Abstract

A layer of sand of thickness h flows down a rough surface if the inclination is larger than some threshold value which decreases with increasing h. A tentative microscopic model for the dependence of on h is proposed for rigid frictional grains, based on the following hypothesis: i) a horizontal layer of sand has some coordination z larger than a critical value z_c, where mechanical stability is lost ii) as the tilt angle is increased, the configurations visited present a growing proportion z_s of sliding contacts. Instability with respect to flow occurs when . This criterion leads to a prediction for in good agreement with empirical observations.