Insight into the Equivalent Shear Strength of Rock Masses with Multiple Nonpersistent Joints based on Laboratory Tests
摘要
The equivalent shear strength (ESS) of a rock mass with multiple nonpersistent joints is a critical input parameter for stability analysis using the equivalent approach. However, accurately evaluating ESS remains a significant challenge in rock mechanics due to the inherent complexity of joints. To gain deeper insight into the ESS, this paper conducts systematic laboratory direct shear tests on rock-like samples, accounting for key geometric parameters such as persistence, inclination angle, and number of nonpersistent joints. By integrating physical observations with microelement mechanical analysis, the mechanism of mechanical degradation of rock bridges under compressive-shear loading is revealed. Furthermore, an improved Jennings criterion for ESS evaluation is derived, incorporating both joint geometric parameters and the mechanical degradation of rock bridges. Validation against experimental data demonstrates that the improved criterion achieves significantly higher accuracy than the original model. These results provide an in-depth understanding of the variables influencing ESS from multiple perspectives. The impact of the geometric parameters of nonpersistent joints on the equivalent shear strength is elaborated. The mechanism of mechanical degradation of rock bridges under compressive‒shear loading is revealed. An improved Jennings criterion is proposed considering the geometric parameters and mechanical degradation.