Malloggi, Florent G.J. (2006) Etudes expérimentales d'avalanches granulaires. PhD thesis Physique des fluide, Physique, ESPCI.

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Abstract

Granular deposits are ubiquitous in nature, they display solid or fluid-like behavior as well as avalanches, mud flows and their catastrophic human and economical toll. The perspective of risk modeling of these phenomena is hindered by the lack of conceptual clarity since the rheology of the particulate flows is poorly understood. In this thesis, we investigate an experimental work on avalanches propagating on an erodible substrate.
In the first part, the stability diagram of the layer deposited on an inclined plane is established, both in the air and in the water. The different steps of the formation of an avalanche front are explained.
The rheology of steady uniform flows of sand is fund and compared to other results obtained in the literature. Experimental measurements, "sooted blade" and "multi-colored layers", show the existence of a static zone under the flow. The previous rheology is changed and the avalanches can be described in term of local rheology. Using this flow rule in the case of solitary erosion waves gives the erosion profile which takes place in the avalanche. The behavior is different for sand and for beads. The sand wave does not erode the substrate down the bottom and the beads wave erodes the entire layer.
In the second part, the stability of those waves is studied. Above a given angle the wave become transversally unstable. After an initial wavelength, there is a coarsening process by fusion. At the final stage the coarsening is ended by fingering. The first instability is linear long wavelength instability. All the wavelengths measured collapse in the same curve when they are scaled by the size of the grains.

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