Rigid intruder inside a two-dimensional dense granular flow: Drag force and cavity formation

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We investigate experimentally the drag force experienced by a rigid intruder immersed in a bidimensional dense and disordered granular flow as well as the displacement fields of grains around it. The approach to jamming is revealed through the drastic increase of force levels as well as the disappearance of the cavity that forms behind the intruder with increasing granular packing fraction. A simple picture based on the compressibility of the granular material is proposed to explain the dependence of the cavity area on the packing fraction, intruder size, and cell width.