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Etude expérimentale de l'équilibre mécanique d'un milieu granulaire : exemples du silo et du tas de sable

Abstract : Experiments show that contact forces in a granular medium are very inhomogeneous and form a network of "force chains" bearing the major part of the stress. This thesis is aimed at understanding how important the force chains are in the description of the mechanical equilibrium properties of a granular material.

Measuring forces in a granular material is tricky due to a fundamental coupling between the sensor deformations and the mobilization of friction forces inside the granular material or at a boundary wall. However, it is possible to get reproducible and significant results when using a well-defined measurement procedure.

We have been interested in studying the links between the structure of the granular packing and the stress distribution. The equilibrium of a granular material in a silo is very sensitive to shearing or vibrations which also affect the structure of the packing as shown by local and average density measurements. Below the apex of a sandpile formed with avalanching grains, we observe a pressure minimum or "dip", but the pressure is a maximum when the grains are deposited in horizontal layers. Residual pressure fluctuations have been measured as a function of the grain size or the filling height of the silo.

Most of our observations are qualitatively and quantitatively well-described by the OSL model where the stresses propagate along two directions, one of them corresponding to the mean direction of force chains. The idea of force propagation allows us to understand the pressure distribution below a sandpile or the shape of the pressure saturation curve in a silo, including the pressure oscillations when there is a surcharge.

We also propose a model of arch hardening which explains the existence of a fragmentation mode when turning a tube filled with grains uspside down.
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https://tel.archives-ouvertes.fr/tel-00258084
Contributor : Loïc Vanel <>
Submitted on : Thursday, February 21, 2008 - 10:13:01 AM
Last modification on : Wednesday, December 9, 2020 - 3:12:27 PM
Long-term archiving on: : Thursday, May 20, 2010 - 6:42:31 PM

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  • HAL Id : tel-00258084, version 1

Citation

Loïc Vanel. Etude expérimentale de l'équilibre mécanique d'un milieu granulaire : exemples du silo et du tas de sable. Analyse de données, Statistiques et Probabilités [physics.data-an]. Université Pierre et Marie Curie - Paris VI, 1999. Français. ⟨tel-00258084⟩

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