Jean-Christophe Géminard

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We investigate the morphology and dynamics of the region invaded by air injected at the bottom of an immersed granular bed. Previous experimental results point out the formation of a fluidized zone with a parabolic shape which does not depend, in the stationary regime, on the injection flow-rate. By tilting the experiment, we can tune the effective gravity(More)
Many volcanoes exhibit temporal changes in their degassing process, from rapid gas puffing to lava fountaining and long-lasting quiescent passive degassing periods. This range of behaviors has been explained in terms of changes in gas flux and/or magma input rate. We report here a simple laboratory experiment which shows that the non-Newtonian rheology of(More)
Triggering large-scale motion by imposing vibrations to a system can be encountered in many situations, from daily-life shaking of saltcellar to silo unclogging or dynamic earthquakes triggering. In the well-known situation of solid or granular friction, the acceleration of imposed vibrations has often been proposed as the governing parameter for the(More)
The injection of gas in a liquid-saturated granular bed gives rise to a wide variety of invasion patterns. Many studies have focused on constrained porous media, in which the grains are fixed in the bed and only the interstitial fluid flows when the gas invades the system. With a free upper boundary, however, the grains can be entrained by the ascending gas(More)
We report on the dynamics of a model frictional system submitted to minute external perturbations. The system consists of a chain of sliders connected through elastic springs that rest on an incline. By introducing cyclic expansions and contractions of the rest length of the springs, we induce the reptation of the chain. Decreasing the amplitude of the(More)
We report a time-resolved study of the dynamics associated with the slow compaction of a granular column submitted to thermal cycles. The column height displays a complex behavior: for a large amplitude of the temperature cycles, the granular column settles continuously, experiencing a small settling at each cycle. By contrast, for a small-enough amplitude,(More)
The mechanical response of a wet granular layer to imposed shear is studied experimentally at low applied normal stress. The granular material is immersed in water and the shear is applied by sliding a plate resting on the upper surface of the layer. We monitor simultaneously the horizontal and the vertical displacements of the plate to submicron accuracy(More)
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