Slowly driven sandpile formation with granular mixtures

We discuss a one-dimensional sandpile model with $N$ different particle types and an infinitesimal driving rate. The parameters for the model are the $N^2$ critical slopes for one type of particle on top of another. The model is trivial when $N=1\mathrm{}$, but for $N=2\mathrm{}$ we observe four broad classes of sandpile structures in different regions of the parameter space. We describe and explain the behavior of each of these classes, giving quantitative analysis wherever possible. The behavior of sandpiles with $N>\mathrm{}2\mathrm{}$ essentially consists of combinations of these four classes. We investigate the model’s robustness and highlight the key areas that any experiment designed to reproduce these results should focus on.