Peak Shear Strength Criterion for Discontinuities with Different Rock Types Based on Revisiting Frictional Angle

Discontinuities with different rock types are widely distributed in the Three Gorges reservoir area, and accurately evaluating the peak shear strengths of them is vital for rock mass stability analysis in this reservoir area. A batch of rock-like joint replicas with the same natural morphology but different joint wall strength combinations is prepared, and direct shear tests are conducted on them under constant normal stresses ranging from 0.3 to 3.0 MPa. Further, the joint wall strength combination coefficient (λ) is introduced to capture the combined effect of rock compressive strength and basic angle on the peak shear strength of discontinuities with different rock types. Testing results illustrate that the peak shear strengths of discontinuities with different rock types decrease non-linearly with increasing λ, and the decrease degree is mainly controlled by roughness while showing no obvious relationship with normal stress. A simple power law function is selected to analyze the correlation between the peak friction angles and λ, and an empirical strength criterion with the inclusion of three-dimensional morphology parameters is developed to predict the peak shear strengths of discontinuities with different rock types. Finally, natural samples collected from the Three Gorges reservoir area are used to further validate the reliability of the new criterion for evaluating the peak shear strength of natural discontinuities with different rock types. To some extent, the new criterion can provide a theoretical basis for the stability evaluation of rock masses containing discontinuities with different rock types in the Three Gorges reservoir area. © 2024 China University of Geosciences. All rights reserved.