Stress distribution and surface instability of an inclined granular layer

Static granular materials may avalanche suddenly under continuous quasi-static drives. The phenomenon, which is important for many engineering applications, can be explained by analyzing stability of elastic solutions. We show this for a granular layer driven by its inclination angle in gravity, of which elastic problem could be solved generally and analytically. It is found that a lost of stability may occur only at free surface of the layer. The result is considered to be relevant for understanding surface avalanches and flows observed by experiments.