Summary
For the rapid shear flow of granular materials with large overburden loads, an action involving the simultaneous impact of more than two particles is shown to provide a mechanism for reducing the effective drag force acting on the flowing material. The drag is reduced below both the static friction value and the drag due only to binary collisions. Since the frequency of multiparticle collisions increase as the bulk density of the flowing material decreases, larger overburdens result in more multiparticle collisions giving rise to greater decreases in the effective drag force. It is hypothesized that this mechanism may account for the extraordinarily long runout distances observed for large rockslides and avalanches. A simple numerical model of interacting inelastic disks in a quasi-two dimensional flow was used to guide the investigation and verify the proposed mechanism.
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Dent, J.D. Flow properties of granular materials with large overburden loads. Acta Mechanica 64, 111–122 (1986). https://doi.org/10.1007/BF01180102
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DOI: https://doi.org/10.1007/BF01180102