The onset of yielding in a granular system

We investigate the mechanical stability of a granular system subjected to shear stress. We use flow pulses of water in a fluidized bed to prepare a granular sample with a specific volume fraction (0.57 $<\phi<$ 0.63) and then shear the grains using a small, embedded plate, observing the force required to unjam the system. An understanding of how the system responds to shear is crucial to constructing a phase diagram for granular materials.