Stratification in poured granular heaps

The stratification of poured granular mixtures into layers according to particle size has long been identified as an important mechanism by which such materials segregate1,2. The implications of this effect for the process industries have also been discussed3,4. Makse et al.5 suggestthat stratification takes place only when there is a marked difference in the shape of large and small grains; specifically, when the angle of repose of the coarse phase is much greater than that of the fines. Our experiments show that stratification can occur in the absence of such heterogeneity of particle shapes within the mixture.