Granular packings of elongated faceted particles deposited under gravity

Abstract

We report experimental and theoretical results of the effect that particle shape has on thepacking properties of granular materials. We have systematically measured theparticle angular distribution, the cluster size distribution and the stress profilesof ensembles of faceted elongated particles deposited in a bidimensional box.Stress transmission through this granular system has been numerically simulatedusing a two-dimensional model of irregular particles. For grains of maximumsymmetry (squares), the stress propagation localizes and forms chain-like forcesanalogous to those observed for granular materials composed of spheres. For thicklayers of grains, a pressure saturation is observed for deposit depths beyond acharacteristic length. This scenario correlates with packing morphology and can beunderstood in terms of stochastic models of aggregation and random multiplicativeprocesses. As grains elongate and lose their symmetry, stress propagation is stronglyaffected. Lateral force transmission becomes less favored than vertical transfer, andhence, an increase in the pressure develops with depth, hindering force saturation.