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Cohesion-induced weakening ? Clues from the failure of a cohesive granular step
The failure of 2D numerical cohesive granular steps collapsing under gravity is simulated for a large range of cohesion. Focusing on the cumulative displacement of the grains, we establish a sensible criterion for capturing the failure characteristics. We are able to locate the failure in time and to identify the different stages of the destabilisation. Defining a narrow displacement interval, a well-defined linear shear band comes out, revealing the failure and its orientation. Solving the equilibrium of the failing block, with gravity, friction and cohesion as sole ingredients, we make simple analytical predictions for the relation between failure angle, friction, and cohesion. In particular, the prediction and the numerical data do agree only in the case of an internal friction decreasing with cohesion, thereby suggesting the existence of a cohesion induced weakening mechanism.