Volume 85, Number 2, January 2009
Article Number 24003
Number of page(s) 5
Section Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics
Published online 22 January 2009
EPL, 85 (2009) 24003
DOI: 10.1209/0295-5075/85/24003

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

M. Wyart

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

received 31 July 2008; accepted in final form 16 December 2008; published January 2009
published online 22 January 2009

A layer of sand of thickness h flows down a rough surface if the inclination is larger than some threshold value $\theta _{start}$ which decreases with increasing h. A tentative microscopic model for the dependence of $\theta _{start}$ 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 zc, where mechanical stability is lost ii) as the tilt angle is increased, the configurations visited present a growing proportion zs of sliding contacts. Instability with respect to flow occurs when z - zs = zc. This criterion leads to a prediction for $\theta _{start}(h)$ in good agreement with empirical observations.

45.70.Ht - Avalanches.
47.57.Gc - Granular flow.

© EPLA 2009