Influence of stress path on excavation unloading response |
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| Affiliation: | 1. School of Civil Engineering, Chongqing University, Chongqing 400030, China;2. Key Laboratory of New Technology for Construction of Cities in Mountain Area, Ministry of Education, Chongqing 400030, China;1. School of Civil Engineering, Chongqing University, Chongqing 400045, China;2. Key Laboratory of New Technology for Construction of Cities in Mountain Area, Ministry of Education, Chongqing 400045, China;3. Taiyuan University of Technology, Taiyuan 030024, China;4. AGECON, Hong Kong, China;1. Advanced Research Center, Central South University, Changsha 410083, China;2. School of Resources and Safety Engineering, Central South University, Changsha 410083, China;1. School of Civil Engineering, Shandong University, Jinan, China;2. School of Civil and Environmental Engineering, Nanyang Technological University, Singapore;3. Department of Civil Engineering, The University of Hong Kong, Hong Kong;1. Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, Northeastern University, Shenyang 110819, China;2. Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Rock Mechanics (LMR), CH-1015 Lausanne, Switzerland |
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| Abstract: | The unloading process of rock mass is critical to the research of excavation disturbances of tunnels in deep mines, and the dynamic effects induced by the release of in situ stress cannot be ignored. In this study, a mathematical physics model was applied to characterise the unloading mechanisms of brittle rock under different stress paths in two dimensions using the universal discrete element code PFC2D for numerical simulations. The excavation relaxation method was employed to control forces applied to the tunnel internal surface to investigate the influence of various in situ stresses, the unloading rate and path on the dynamic effects. Longer unloading time can mitigate the dynamic effects within a certain time range. Nonlinear unloading paths prevail over the linear path in releasing kinetic energy. Furthermore, the exponential path that represents “slow followed by fast” unloading induces the most peripheral displacement, while the cosine path that represents “fast followed by slow” unloading yields the most cracks around the tunnel. The results also indicated that increasing the ratio of horizontal and vertical in situ stresses can exacerbate the dynamic effects. The proposed model agreed well with the theoretical solution and provided a basis for understanding the evolution of the unloading response around the tunnel. |
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| Keywords: | Rock mass Stress path Stress release rate Unloading process Dynamic response |
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