Brittle failure of rockslides linked to the rock bridge length effect

A rock bridge along the potential sliding surface of a rockslide has a relatively large bearing capacity and governs the stability of the rock slope. The physical and mechanical properties of specimens representing four rock bridge lengths were researched by direct shear experimentation. The micromechanism associated with the change in shear strength parameters was analyzed by PFC2D numerical simulations that corresponded to the experiments. The results revealed a rock bridge length effect, through which the peak shear strength increases with rock bridge shortening, accompanied by an increase in cohesion and a decrease in internal friction angle and main fracture surface roughness. Rock bridge shortening decreased the density of the microcracks at the shear stress peak point, changing the cohesive strength and frictional strength. The decrease in the internal friction angle could change the critical stress intensity factors to make shear cracks preferentially initiate over tensile cracks. Fracture roughness therefore decreased, inducing a lower residual shear strength. As a result, the difference in the peak and residual strengths increased with rock bridge shortening, which would promote brittle failure of the corresponding rock slope.