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Theses

Dynamique des Avalanches

Abstract : Granular matter can remain static with an inclined free surface up to a critical angle where it starts flowing spontaneously. The dynamics of the resulting surface flow is governed by the mobilization and deposition of grains. In spite of its practical importance, little is known about the dynamics of this transition. In this thesis, the problem is studied in two different geometries of granular flows. In the first experiment, a layer of sand on a rough plane is tilted until its equilibrium becomes metastable, so that a local perturbation triggers an avalanche. The measurement of the perturbation threshold shows that the static-moving transition is sub-critical. The avalanche dynamics and shape result from a permanent mass exchange with the layer, mobilizing at the head front and depositing at the rear front. Surprisingly we observe a saturation of the amplitude, which can be related to the presence of the solid plane. We show the existence of two types of avalanches, a first which mobilizes the layer only downhill from the origin, leaving a triangular track, and a second which destabilizes the entire layer through an upward propagating front. The underlying mechanisms turn out to be different. The second experiment on the transient flow leading to the formation of a pile shows the strong influence of the initial preparation. Two effects are studied, one associated with the packing density, and the other to an anisotropic «texture» acquired during preparation. The last part presents some models describing the observed avalanches. As a conclusion, a continuous model for granular surface flows is developed on the basis of the reported results. We use a system of depth-averaged conservation equations with an evolving static/mobile boundary.
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https://tel.archives-ouvertes.fr/tel-00003998
Contributor : Adrian Daerr <>
Submitted on : Wednesday, December 17, 2003 - 7:15:11 AM
Last modification on : Thursday, December 10, 2020 - 12:39:00 PM
Long-term archiving on: : Friday, April 2, 2010 - 7:08:07 PM

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  • HAL Id : tel-00003998, version 1

Citation

Adrian Daerr. Dynamique des Avalanches. Physique [physics]. Université Paris-Diderot - Paris VII, 2000. Français. ⟨tel-00003998⟩

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