DEM analysis of rock bridges and the contribution to rock slope stability in the case of translational sliding failures

International audienceIn the presence of joint sets sub-parallel to a slope face, the stability of the rock mass is assumed to be controlled by the shear strength along the joints. If the joints are persistent, the shear strength can be assessed according to the Mohr-Coulomb criterion with appropriate values for the cohesion and the friction angle on the associated surface. If the joints are non-persistent with their continuity being interrupted by the presence of rock bridges, their apparent strength increases considerably. In this case, the contribution of the rock bridges has to be accounted for in the stability analysis. Jennings' formulation is considered to be one of the first rock slope stability analysis that evaluates the resistance to sliding as a weighted combination of both intact rock and joint planes strengths. The present study discusses the validity of Jennings' formulation. The progressive failure of a rock slope involving a non-persistent joint is numerically investigated based upon simulations performed using a Discrete Element Method specifically enhanced to model jointed rock masses. The intact material is represented as an assembly of bonded particles. Pre-existing discontinuities are explicitly included in the model by using a modified contact logic that ensures an explicit and constitutive mechanical behaviour of the joint planes. The failure of the rock bridges is simulated through the breakage of the inter-particle bonds. In addition, rock bridges can be spatially distributed along the sliding surface following a prescribed spatial probabilistic distribution. The respective contribution of spatial distribution of rock bridges over the main sliding plane, the dip angle of that plane and the location of the centre of gravity of the likely unstable block were investigated through a series of numerical simulations and the results systematically compared to Jennings' predictions. The limit of Jennings' formulation appears as soon as tensile failure becomes predominant and an alternative formulation is proposed to assess the resulting equivalent strength