Experimental study of granular stratification

The flow of binary granular mixtures made of sand (rough) and glass spheres (smooth) into a vertical Hele Shaw cell give rises to heaps exhibiting different internal structures. We first give the phase diagram of heap morphologies classified as a function of the size ratio of rough to smooth particles. Granular stratification is one type of observable structure, which consists in the formation of alternating layers through the pile, and is found to occur only for a size ratio greater than 1.5. We present an experimental study of stratification and report that the wall separation and the mass flux can modify the layering process.