Abstract
We experimentally investigate the deformation of a granular material submitted to a localised compression force. The strain field is characterised using a near field Diffusing-Wave Spectroscopy technique. The results of point load experiments on an elastic sample are first presented to illutrate the possibilities of the technique. Then, we report new results concerning the behaviour of a granular medium, showing a non-linear response with the force increment and a spatial repartition of the strain that differs from elasticity. Moreover, we analyse the partial reversibility of the deformation after a loading/unloading cycle in terms of both elastic and plastic contributions.