Kinks and logarithmic tails as stability markers in binary granular piles

Abstract

Stability is typically gauged using the angle of repose which assumes that the heap formed after an event follows a straight line - a case that is rarely true. Here, we demonstrate that a single parameter measuring the slope concavity ℓ_e allows a more complete description of stability of the granular medium. We validate using cellular automata model and experiments that the sign and magnitude of ℓ_e captures the enhancement or decrease of solidity resulting from granular mixing. Moreover, regions with highly negative ℓ_e tend to have a more frequent occurrence of vertical slopes - indicating a highly stable pile.