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A statistical model of contacts and forces in random granular media

We present a statistical model of contact angles and force correlations in granular media with and without friction. The model is motivated by recent measurements of the contact angles and is based on force balance, geometric, and static friction constraints. It reveals preferential alignment of the two largest forces on a grain, which give rise to chain-like force correlations. The dependence of the inter-force angle distributions on coordination number, minimum angle between contacts, space dimension, and stress anisotropy is investigated. The numerical results show qualitative agreement with earlier experiments and simulations, suggesting the importance of the contact geometry in understanding the spatial arrangement of forces in packing.