Evaluation of the Crack Propagation Capacity of Hard Rock Based on Stress-Induced Deformation Anisotropy and the Propagation Angle of Volumetric Strain

The occurrence of various types of disasters in deep underground engineering is related not only to the strength of the rock mass but also to the crack propagation capacity (CPC) under corresponding stress conditions. The deep-seated rock mass is generally in the stress state of σ1 > σ2 > σ3, and the CPC under differential stress is very important to evaluate the brittle failure of rock. Therefore, based on the deformation characteristics of Baihetan (BHT) basalt under true triaxial compression (TTC), the evaluation index (IP) of the CPC is established, which considers the characteristics of stress-induced deformation anisotropy and the propagation angle of volumetric strain. The evaluation indexes of JP marble, BS granite and BHT basalt under TTC are analysed and compared. When the stress exceeds the crack initiation stress, the evaluation index of the CPC decreases with the increase of σ2, but increases with the increase of σ3, and the effect of σ3 on the CPC index is greater than that of σ2. Under TTC, the CPC of JP marble is the largest, followed by that of BS granite and BHT basalt. The analysis shows that the evaluation index (IP) proposed in this study is also suitable for conventional triaxial compression and uniaxial compression conditions. In addition, the test result shows that there is divisibility between the failure mode and IP under TTC. The relationship between IP and the failure mode of BHT basalt shows that splitting failure occurs when IP < 0.3, that shear failure occurs when IP > 0.4, and mixed failure occurs when IP is between these values. The evaluation index of the CPC proposed in this paper can provide a theoretical reference for evaluating the failure of surrounding rock near the opening boundary of deep underground rock engineering.