Origin of a repose angle: kinetics of rearrangement for granular materials.

A microstructural theory of dense granular materials is presented, based on two main ideas: first, that macroscopic shear results from activated local rearrangements at a mesoscopic scale; second, that the update frequency of microscopic processes is determined by granular temperature. In a shear cell, the resulting constitutive equations account for Bagnold's scaling and for the existence of a Coulomb criterion. In a granular flow down an inclined plane, they account for the rheology observed in experiments [Phys. Fluids 11, 542 (1999)]] and for temperature and velocity profiles measured numerically [Europhys. Lett. 56, 214 (2001)]] [Phys. Rev. E 64, 051302 (2001)]].