Motion of an Intruder Through a Two Dimensional Disordered Granular Medium

We measured simultaneously the drag force on a cylindrical object (intruder) induced by the flow of a dense 2D bidisperse granular material around it, and the displacements of the individual grains. This type of experiment provides a way to examine the local rheological properties of the material. We found that the measured drag force increases sharply with the packing fraction near φ *=82.35%, indicating a transition to jamming. The dependence of the drag force on φ is clearly related to a decrease in the area of the empty cavity that forms behind the intruder.