Response of a noncohesive packing of grains to a localized force: deviation from continuum elasticity.

In order to characterize the mechanical behavior of grain piles, we investigate the response of a noncohesive two-dimensional packing of cylinders submitted to a localized force. By means of image processing, we obtain an accurate measurement of the individual grain displacements in the reversible regime of deformation. The measured displacement field deviates unambiguously from the predictions of linear elasticity and of other theoretical descriptions commonly used to model the behavior of cohesionless soils in civil engineering or in soil mechanics. Surprisingly, the analysis of the deformation field reveals a tendency to localization in the reversible regime.