POSSIBLE STRATIFICATION MECHANISM IN GRANULAR MIXTURES

We propose a mechanism to explain what occurs when a mixture of grains of different sizes and different shapes (i.e., different repose angle s) is poured into a quasi-two-dimensional cell. Specifically, we devel op a model that displays spontaneous stratification of the large and s mall grains in alternating layers. We find that the key requirement fo r stratification is a difference in the repose angles of the two pure species, a prediction confirmed by experimental findings. We also iden tify a kink mechanism that appears to describe essential aspects of th e dynamics of stratification.