Shearing of jammed granular systems with fixed pinning sites

The rheology of granular media is characterized in part by shear jamming, in which shearing of collections of individual grains under confinement leads to a transition from fluid-like to solid-like behavior. Such systems are driven by the boundaries and exhibit anisotropic force networks and history-dependent behavior. Here we experimentally investigate planar shear of an athermal, granular system with small pins inserted within the shearing zone which act as fixed obstacles within the bulk. We use photoelastic grains to visualize the stress networks and particle tracking to characterize particle locations and kinematics. We characterize the mean flow and stress response when small numbers of pinning sites are present in the system. We find that these pins can act as additional supports to stabilize the stress network and enhance anisotropy based on their arrangement. Such experiments represent a step to exploring the effects of pinning lattices which may offer a route to tunable granular rheology.