  The failure of 2D numerical cohesive granular steps collapsing under gravity
are simulated for a large range of cohesion. Focussing on the cumulative
displacement of the grains, and defining a displacement threshold, 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. We find that the onset of the failure is delayed by increasing
cohesion, but its duration becomes shorter. Defining a narrow displacement
interval, a well-defined shear band revealing the failure comes out. Solving
the equilibrium of the failing block, we are able to make successful
predictions for the dependance between failure angle and cohesion, thereby
disclosing two distinct frictional behaviour: while friction remains constant
at small cohesion, it significantly decreases with cohesive properties at
larger cohesion. The results hence reveal two regimes for the behaviour of
cohesive granular matter depending on cohesion strength, revealing a
cohesion-induced weakening mechanism.
