ONSET OF GRANULAR FLOWS ON AN INCLINED ROUGH-SURFACE - DILATANCY EFFECTS

The onset of the flow of a two-dimensional granular material resting o n an inclined rough surface is studied in both experiments and numeric al simulations. The critical angle theta(c) at which the particles sta rt to how is found to increase when the initial thickness of the layer decreases, showing that the strength of the material, i.e. the intern al friction angle, is greater near the rough surface than in the bulk. This phenomenon is shown to be connected to the dilatancy occurring i n the medium when it starts to how: in a thin layer of material the ri gidity of the surface prevents local rearrangements of the particles a nd thus imposes a greater level of dilatancy, leading to a larger effe ctive friction angle. This robust effect is also observed with three-d imensional granular materials involving irregular shaped particles.