Tunnel failure in hard rock with multiple weak planes due to excavation unloading of in-situ stress
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Tunnel failure in hard rock with multiple weak planes due to excavation unloading of in-situ stress CHEN Shao-jie(陈绍杰)1, FENG Fan(冯帆)1, 2, 3, WANG Ya-jun(王亚军)2, LI Di-yuan(李地元)4, HUANG Wan-peng(黄万朋)1, ZHAO Xing-dong(赵兴东)3, JIANG Ning(江宁)1 1. College of Energy and Mining Engineering, Shandong University of Science and Technology, Qingdao 266590, China; 2. State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China; 3. School of Resources and Civil Engineering, Northeastern University, Shenyang 110819, China; 4. School of Resources and Safety Engineering, Central South University, Changsha 410083, China © Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract: 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. Key words: rock tunnel; weak planes; excavation unloading; crack propagation; energy evolution; finite element method/discrete element method (FEM/DEM) Cite this article as: CHEN Shao-jie, FENG Fan, WANG Ya-jun, LI Di-yuan, HUANG Wan-peng, ZHAO Xing-dong, JIANG Ning. Tunnel failure in hard rock with multiple weak planes due to excavation unloading of in-situ stress [J]. Journal of Central South University, 2020, 27(10): 2864−2882. DOI: https://doi.org/10.1007/s11771-020-4515-7.
1 Introduction The stability of deep underground openings
and tunnels depends on the ability of the stratum (e.g., rock mass) to withstand concentrated stresses at the wall [1]. When an underground opening is excavated, the tangential stre
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