From thin to thick granular surface flows: The stop flow problem

The surface evolution of a sandpile was investigated theoretically by Bouch aud ed al. several years ago [J. Phys. I 4, 1383 (1994)]. Their model assum es that the erosion/accretion rate of the static grains is proportional to the local amount R of rolling species, de Gennes et al. [Phys. Rev. E 58, 4 692 (1998)] have noticed recently that this assumption must be modified for thick surface flows, where the,rate should become less dependent on R. In order to analyze the progressive transition from thin to thick flows, we fo cus on the so-called stop flow problem, where an incoming front of rolling particles suddenly hits an immobile wall. We find that the physical behavio r of the grains changes significantly as the thickness of the incoming fron t increases. [S1063-651X(98)08412-8].