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

– A layer of sand of thickness h flows down a rough surface if the inclination is larger than some threshold value θstart which decreases with h. A tentative microscopic model for the dependence of θstart with 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 θstart(h) in good agreement with empirical observations. On the dependence of the avalanche angle on the granular