Surface Fluidization of a Sand Pile

We investigate the capability exhibited by a vibrated sand pile to creep up into a vessel. Our measures demonstrate that the fluidization of a heap submitted to vertical vibrations of high enough amplitude is confined to an upper layer the thickness of which depends on the amplitude Γ of the variations of the acceleration to which the pile is submitted. The internal part of the heap remains compacted due to a joint action of the gravity force and of kinetic-energy losses due to either internal friction or grain-grain collisions.