Effects of natural stiff discontinuities on the deformation and failure mechanisms of deep hard rock under true triaxial conditions

Stiff discontinuities have a significant influence on deep hard rock engineering disasters. To study the influence of these discontinuities on the deformation and failure mechanisms of deep hard rock during excavation, true triaxial tests are carried out on marble samples with natural stiff discontinuities; samples with different discontinuity inclination angles and thicknesses are tested under different true triaxial stress conditions. The experimental results show that the post-peak deformation and failure characteristics of a sample are significantly influenced by the inclination angle, thickness, and stress state of the stiff discontinuity. Under the conditions of a relatively high minimum principal stress, small intermediate principal stress, thick stiff discontinuity, and inclination angle close to the failure angle of the intact sample at the same stress level, the propagation and penetration of microcracks inside the sample are mainly controlled by the stiff discontinuity, and the sample is more prone to sudden and violent tensile failure along the stiff discontinuity. Based on these experiments, a sudden and violent failure tendency index of deep hard rock with a stiff discontinuity (psi) is proposed to evaluate the impact of stiff discontinuities on surrounding rock failure in deep engineering, and the characteristics of psi under typical stress levels are summarized. This research can provide a reference for the prevention and control of sudden disasters caused by stiff discontinuities in deep engineering.