Modeling avalanches in granular matter

Sand is a complex material. At rest, a sand pile is a solid. But as soon as the external stress exceeds a certain threshold, it starts flowing like a liquid. During an avalanche, the two states coexist: a liquid phase rolls on the top of a solid phase, the latter is the result of the sedimentation of the liquid phase. The global description of the rheology of the granular material is still a open question and an active field of research.
In 1994, Bouchaud et al. developed a phenomenological description of the complex interactions between the two phases for starting avalanches. Inspired by this approach, we build a new description of the physics of an avalanche, and applied it to the collapse of a granular column. We the compare our theoretical predictions to 3D DEM numerical simulations and experiments for various granular materials.