Boundary conditions and event scaling of granular stick-slip events

We describe experiments on stick-slip failure of a granular material within a linear shear cell. The experiments are performed in a quasi-two-dimensional photoelastic granular material which is sheared via a slider block and spring moving at a constant velocity. The apparatus can provide either constant-volume or constant dP/dV boundary conditions on the aggregate, and we observe boundary-condition dependence in various size-characterizations (duration, force drop, maximum velocity, energy released, area) of the events. Through the use of photoelastic particles, we visualize force chains before and after stick-slip events. We observe that patterns of slip and stress release are highly heterogeneous in their spatial extent, and associate this with scatter in the scaling relations.