Acoustic Probing of the Jamming Transition in an Unconsolidated Granular Medium

TL;DR

This study uses acoustic waves to probe the elastic properties of unconsolidated granular media near the jamming transition, revealing pressure-dependent elastic moduli and confirming theoretical predictions about shear rigidity scaling.

Contribution

It provides experimental validation of theoretical models on granular elasticity and uncovers unexpected pressure dependence of the bulk modulus.

Findings

Elastic moduli depend on pressure near jamming transition.

Shear rigidity scales with pressure as predicted by theory.

Bulk modulus shows similar pressure dependence to shear modulus.

Abstract

Experiments with acoustic waves guided along the mechanically free surface of an unconsolidated granular packed structure provide information on the elasticity of granular media at very low pressures that are naturally controlled by the gravitational acceleration and the depth beneath the surface. Comparison of the determined dispersion relations for guided surface acoustic modes with a theoretical model reveals the dependencies of the elastic moduli of the granular medium on pressure. The experiments confirm recent theoretical predictions that relaxation of the disordered granular packing through non-affine motion leads to a peculiar scaling of shear rigidity with pressure near the jamming transition corresponding to zero pressure. Unexpectedly, and in disagreement with the most of the available theories, the bulk modulus depends on pressure in a very similar way to the shear modulus.