Onset of Granular Flows on an Inclined Rough Surface: Dilatancy Effects

(Received 6 December 1995, received in final form 19 February 1996, accepted 27 February 1996)

Abstract
The onset of the flow of a two-dimensional granular material resting on an inclined rough surface is studied in both experiments and numerical simulations. The critical angle at which the particles start to flow is found to increase when the initial thickness of the layer decreases, showing that the strength of the material, i.e. the internal friction angle, is greater near the rough surface than in the bulk. This phenomenon is shown to be connected to the dilatancy occurring in the medium when it starts to flow: in a thin layer of material the rigidity of the surface prevents local rearrangements of the particles and thus imposes a greater level of dilatancy, leading to a larger effective friction angle. This robust effect is also observed with three-dimensional granular materials irregular shaped particles.