EXPERIMENTAL STUDIES OF STRATIFICATION IN A GRANULAR HELE-SHAW CELL

We show that, when a mixture of small and large grains is simply poure d in a 'granular Hele-Shaw cell' (two transparent slabs separated by a gap of about 5 mm), the grains spontaneously stratify in alternating layers of small and large grains parallel to the surface of the pile. The spontaneous self-stratification occurs only when the large grains have a larger angle of repose than the small grains do. Conversely, we obtain only spontaneous self-segregation, that is the large grains ar e found preferentially near the bottom of the cell while the small gra ins are found near the top, when the large grains have a smaller angle of repose than the small grains. The observed stratification might be of relevance to explain similar stratified patterns observed in Aeoli an rocks.