Influence of asperity morphology on failure characteristics and shear strength properties of rock joints under direct shear tests

The asperitymorphology has profound influences on the failure characteristics and shear strength of rock joints. To investigate these influences, degradation characteristics and mechanical properties were studied based on direct shear tests conducted on six groups of artificial rock joints with regular profiles. For each group of joints, the joint profile consisted of several asperities with a particular amplitude and inclination angle. After completion of shear tests, the degradation of asperities was analyzed and interpreted by the following four types of failure modes: frictional sliding, incomplete shear-off, complete shear-off, and tensile cutoff. The results revealed that in addition to the applied normal stress, both the amplitude and inclination angle had an important influence on the occurrence of the failure modes. Experimental results showed that the peak shear displacements of all joints were far less than the base length of asperities, and the peak shear displacement rate had a mean of 2.04%, indicating that the peak shear strength wasmobilized at a very small shear displacement. The peak shear strength and peak friction angle were found to increase with increasing inclination angle in a moderate range up to a certain angle due to sliding and shear failure mechanisms. With further increase of the inclination angle, the asperities tended to failure under tensile mode and resulted in a decreasing trend of both the shear strength and peak friction angle. Experimental results showed that the amplitude had a positive correlation with the strength of rock joints. An existing theoretical model was extended to explain the mechanism behind the aforementioned phenomena observed through laboratory experiments. The results of this study are beneficial for understanding the shear mechanism and the importance of considering both the inclination angle and amplitude in the mechanical behavior of rock joints.