Assessing the shear behavior of rock discontinuities under high temperatures is crucial for the stability of deep underground engineering. In this study, direct shear tests were conducted on granite discontinuities with quantified three-dimensional roughness under various normal stresses (3.0 to 7.5 MPa) and temperatures (25℃ to 800℃). The results indicate that as temperature increases, the failure mode of the discontinuities transitions from brittle asperity shearing to a more ductile state, characterized by a significantly delayed peak shear displacement at 800℃. Furthermore, the peak shear strength, cohesion, and internal friction angle exhibit significant non-linear degradation due to thermally induced microcracking and asperity softening. However, the rough discontinuities still retain a residual level of interlocking and frictional resistance even at extremely high temperatures. To mathematically capture this mechanism, a modified Mohr-Coulomb empirical model was proposed by introducing an exponential thermal damage factor. Validation against the experimental data demonstrated that the proposed model can accurately predict the shear strength degradation, providing a practical and reliable tool for the safety assessment of high-temperature rock mass engineering.
 

Granite discontinuity,• Thermal Treatment,Shear behavior,Empirical model