Pulling an object out of a granular material: Effect of boundaries

We consider controlled failure experiments where a circular intruder is buried at a depth D in a quasi-two-dimensional granular material of photoelastic discs. Under gradually increasing upward pulling force, F, a steadily strengthening granular network forms to the point of failure. Once failure begins, the buried intruder is pulled rapidly out of the material. In a first study, the experiments were done in a very wide container, of width W so that the distance between the intruder and the side boundaries was big enough that boundary effects were minimal. In this case, as F was increased towards failure, a fan-shape network of force chains much wider than the intruder formed above the intruder. In a second study, we steadily decreased W and changed the friction on the sidewalls. For smooth walls, there was no change with decreasing W in the force at failure, F(D). However, for rough walls, there was a clear change in F(D). This talk will present details of the force networks and mechanical response for these experiments. Parallel studies on a 3D version of this experiment will be presented by Jalali et al.