Stress Transmission through a Cohesionless Material

We apply a point load onto a bidimensional packing of elastic grains. The internal state of stress is accessed by means of photoelastic visualization. The region in which the stress response is confined exhibits a parabolic profile. This evidence supports the parabolic nature of the equations describing the stress transmission. Our results oppose classical elasto-plastic models of continuum mechanics, and other recent hyperbolic proposals.