Influence of Weak Interlayer Filling State on the Failure Patterns of Natural Rock Joints

Weak interlayers determine the strength and stability of a jointed rock mass. The influence of weak interlayer filling state on the shear strength and failure patterns of a rock mass was studied by direct shear testing. Two different shear failure patterns of infilled joints were discovered, depending on the filling conditions of the weak interlayer. Shear failure occurred within the weak interlayer for large filling thickness, while the coupling effects of occlusal failure of asperities and shear failure of weak interlayer occurred for thin filling thickness. The shear strength of the infilled rock mass depended on the shear strength of weak interlayers and the occlusal strength of asperities on the rough joints. Moreover, the shear strength of a weak interlayer was entirely utilized in the first stage of shearing, and the occlusal strength of asperities then became much important with increasing shear deformation. The Mohr–Coulomb criterion was adopted to study the relationship between the peak stress and the normal stress in the first and third stages of shear stress evolution, which confirmed that the apparent cohesion and internal friction angle severally controlled the shear strength of the rock mass under low and high normal stresses. Finally, the impact of filling thickness on the shear strength of a jointed rock mass was predicted, according to the variations of apparent cohesion and internal friction angles. Observable shear displacement, accompanied by the secondary growth of shear stress, may be generated in an infilled rock mass before catastrophic failure. The results were of great significance for understanding the influence of the weak interlayer filling state on the shear strength and failure patterns of a jointed rock mass. Monitoring the stress and deformation of the infilled rock mass could provide useful information for the prediction of engineering disasters in rock, allowing effective control measures to be taken before hazards occur.