Tunnel failure in hard rock with multiple weak planes due to excavation unloading of in-situ stress

• Published in: Journal of Central South University Vol. 27; no. 10; pp. 2864 - 2882
• Main Authors: Chen, Shao-jie, Feng, Fan, Wang, Ya-jun, Li, Di-yuan, Huang, Wan-peng, Zhao, Xing-dong, Jiang, Ning
• Format: Journal Article
• Language: English
• Published: Changsha Central South University 01.10.2020; Springer Nature B.V
• Subjects: Crack propagation; Discrete element method; Dynamic response; Energy distribution; Engineering; Excavation; Failure modes; Finite element method; Inclination angle; Kinetic energy; Marble; Metallic Materials; Parametric analysis; Propagation modes; Rock masses; Shearing; Stability; Tectonics; Triaxial compression tests; Underground construction; rock tunnel; 裂纹扩展; crack propagation; weak planes; 能量演化; 开挖卸荷; 硬岩巷道; excavation unloading; energy evolution; 弱面; finite element method/discrete element method (FEM/DEM); 有限元/离散元耦合数值模拟
• ISSN: 2095-2899; 2227-5223
• DOI: 10.1007/s11771-020-4515-7

Natural geological structures in rock (e.g., joints, weakness planes, defects) play a vital role in the stability of tunnels and underground operations during construction. We investigated the failure characteristics of a deep circular tunnel in a rock mass with multiple weakness planes using a 2D combined finite element method/discrete element method (FEM/DEM). Conventional triaxial compression tests were performed on typical hard rock (marble) specimens under a range of confinement stress conditions to validate the rationale and accuracy of the proposed numerical approach. Parametric analysis was subsequently conducted to investigate the influence of inclination angle, and length on the crack propagation behavior, failure mode, energy evolution, and displacement distribution of the surrounding rock. The results show that the inclination angle strongly affects tunnel stability, and the failure intensity and damage range increase with increasing inclination angle and then decrease. The dynamic disasters are more likely with increasing weak plane length. Shearing and sliding along multiple weak planes are also consistently accompanied by kinetic energy fluctuations and surges after unloading, which implies a potentially violent dynamic response around a deeply-buried tunnel. Interactions between slabbing and shearing near the excavation boundaries are also discussed. The results presented here provide important insight into deep tunnel failure in hard rock influenced by both unloading disturbance and tectonic activation.