Abstract
Underground excavation normally causes instability of the mother rock due to the release and redistribution of stress within the affected zone. For gaining deep insight into the characteristics and mechanism of rock crack evolution during underground excavation, laboratory tests are carried out on 36 man-made rock specimens with single or double cracks under two different unloading conditions. The results show that the strength of rock and the evolution of cracks are clearly influenced by both the inclination angle of individual cracks with reference to the unloading direction and the combination geometry of cracks. The peak strength of rock with a single crack becomes smaller with the inclination angle. Crack propagation progresses intermittently, as evidenced by a sudden increase in deformation and repeated fluctuation of measured stress. The rock with a single crack is found to fail in three modes, i.e., shear, tension–shear, and splitting, while the rock bridge between two cracks is normally failed in shear, tension–shear, and tension. The failure mode in which a crack rock or rock bridge behaves is found to be determined by the inclination angle of the original crack, initial stress state, and unloading condition. Another observation is that the secondary cracks are relatively easily created under high initial stress and quick unloading.
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Acknowledgments
This work is supported by the National Natural Science Foundation of China (No. 41130745 and No. 41172243), the Fundamental Research Funds for the Central Universities (No. CDJZR12205501), and the Open Foundation of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection (No. SKLGP2011K003). The authors are deeply grateful to Dr. Yanrong Li of AGECON Ltd. (Hong Kong) for his valuable comments on and constructive revision of the paper, and stimulating discussions on the research.
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Huang, R.Q., Huang, D. Evolution of Rock Cracks Under Unloading Condition. Rock Mech Rock Eng 47, 453–466 (2014). https://doi.org/10.1007/s00603-013-0429-0
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DOI: https://doi.org/10.1007/s00603-013-0429-0