A layer of sand of thickness h flows down a rough surface if the inclination is larger than some threshold value start which decreases with increasing h. A tentative microscopic model for the dependence of 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 start(h) in good agreement with empirical observations.
ASJC Scopus subject areas
- Physics and Astronomy(all)