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DY: Fachverband Dynamik und Statistische Physik
DY 1: Focus Session: Dense Granular Flow
DY 1.4: Invited Talk
Monday, March 14, 2011, 12:00–12:30, HÜL 186
Erosion and mobility in granular avalanches over sloping beds — •Anne Mangeney1, Olivier Roche2, Oldrich Hungr3, and Nicolas Mangold4 — 1IPGP et Unviversité Paris Diderot, Paris, France — 2LMV, IRD, Université de Clermont, Clermont Ferrand, France — 3University of British Columbia, Vancouver, British Columbia, Canada — 4LPGN, Université de Nantes, CNRS, France
We describe laboratory experiments of granular material flowing over an inclined plane covered by an erodible bed, designed to mimic erosion processes of natural flows. Two controlling parameters are the inclination of the plane and the thickness of the erodible layer. We show that erosion processes can increase the flow mobility of the grains by up to 40%. Erosion efficiency is shown to strongly depend on the slope of the topography. Entrainment begins to affect the flow at inclination angles exceeding a critical angle. Runout distance increases almost linearly as a function of the thickness of the erodible bed, suggesting that erosion is mainly supply dependent. Two regimes are observed during granular collapse: a first spreading phase with high velocity followed by a slow thin flow, provided either the slope or the thickness of the erodible bed is high enough. Surprisingly, erosion affects the flow mostly during the deceleration phase and the slow regime. The avalanche excavates the erodible layer immediately at the flow front. Waves are observed behind the front that help to remove grains from the erodible bed. Finally, simple scaling laws are proposed making it possible to obtain a first estimate of the deposit and emplacement time of a granular collapse over erodible bed.