ABSTRACT
Two different experiments are reported. In both cases, the mechanical response of a granular packing submitted to a point load is investigated. In the first experiment we deal with the reversible deformation of a model packing made of discrete square grains in contact. The internal state of stress is accessed by the means of photoelastic visualization. In the second experiment, the sample consists of a thick layer of sand, and grain displacements are recorded. In both case the strained region is confined into parabolic boundaries. These results seem rather in agreement with equations of parabolic nature to describe the stress transmission, and to contradict the classical elasto-plastic modelling of continuum mechanics.
