Stress fluctuations and shear zones in quasistatic granular chute flows

Experimental investigations of quasistatic flows of a two-dimensional granular material comprised of circular cylindrical rods are described. The flows are confined by two rough, parallel walls that can be inclined to the vertical direction. It is observed that boundary layers develop next to the sidewalls and are approximately 5 particle diam. thick, regardless of the width of the channel. The flows are analyzed by means of a modification of Coulomb theory that takes into account stress fluctuations that arise as a result of the ''granularity'' of the flowing material. We propose a probabilistic model where the stress fluctuations play the role of temperature, and the difference between the shear stress and yield stress plays the role of an energy barrier that the system has to overcome in order to yield. The velocity profiles predicted by the model are in agreement with the experiments for both vertical and inclined bins.