Influence of bottom roughness and ambient pressure conditions on the emplacement of experimental dam-break granular flows

International audienceGeophysical granular flows occur at the surface of the Earth and other planets with reduced atmospheric pressure. In this paper, we investigate the run-out of dam-break flows of particle-air mixtures with fine ( d = 75 μm ) or coarse ( d = 150 μm ) grains in a flume with different bottom roughness ( ) and vacuum degrees ( P∗ ). Our results reveal an increase of the flow run-out as d∕ decreases for fine d = 75 μm-particles, and run-out decreases with the dimensionless ambient pressure ( P∗ ) for a given d∕ . In contrast, the run-out for coarser d = 150 μm-particles, is almost invariant respect to P∗ and d∕ . These results show that autofluidization of fine-grained flows demonstrated by earlier works at ambient pressure also occurs at reduced pressure though being less efficient. Hence, autofluidization is a mechanism, among others, to explain long run-out of geophysical flows in different environments