Jamming transition in plowed granular media

We demonstrate in a three-dimensional laboratory plate drag experiment that a granular medium (250~$\mu$m glass beads) exhibits a bifurcation from fluid-like to jammed flow as the volume fraction ($\phi$) is increased above a critical value $\phi_c=0.603 \pm 0.0025$. We measure the force $F_d$ on a flat plate (3.8~cm width, 10.0~cm depth) dragged at constant velocity $v$ through the surface of a granular medium for $0.57<\phi<0.63$. For $\phi<\phi_c$, $F_d$ is independent of time and particle image velocimetry indicates that the flow of the granular media is uniform around the plate. For $\phi>\phi_c$, $F_d$ displays large periodic fluctuations which correspond to the formation of shear bands. Surface profile measurement of the post-drag net displaced volume $\Delta V$ of the granular material reveals that the medium compacts ($\Delta V<0$) in response to drag for $\phi<\phi_c$ and expands ($\Delta V>0$) for $\phi>\phi_c$. Thus the transition to jammed flow at $\phi_c$ is marked by the onset of dilation in granular media.