Sandpiles on fractal bases: pile shape and phase segregation

Sandpiles have become paradigmatic systems for granular flow studies in statistical physics. New directions of investigations are discussed here. Rather than varying the nature of the pile (sand, salt, rice,..) we have investigated changes in the boundary conditions. We have investigated experimentally and numerically sandpile structures on bases having a fractal perimeter. This type of perimeter induces the formation of a quite complex set of ridges and valleys. A screening effect of the valleys is observed and depends on the angle of repose. Binary granular systems have also been investigated on such bases: a spectacular demixing is obtained along the valleys. This type of phase segregation is discussed with respect to numerical studies.