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Abstract
The service tunnel of Jinping Second Stage Hydropower Station, which is covered by over 2 000 m thick rock mass and has a maximum principle stress of over 60 MPa, is used as an example to investigate laws, characteristics, ranges and velocity of stress redistribution with time along directions of parallel and perpendicular to the tunnel axes and balance time of stress field using a numerical analysis method, based on the Kelvin–Voigt–CWFS model, which is a viscoelastoplastic combination model and is adaptable for describing time dependant characteristics of hard and brittle rock mass. The result shows that the stress initially increases and then decreases gradually at the two side walls and decreases quickly at the vault. Their principal vectors rotate gradually during the stress redistribution and 90% adjustment of stress is redistributed in as early as the first several days after excavation. At equilibrium, the stress initially increases and then decreases to stability at the two side walls and increases gradually to the original stress state at the vault with increasing distance from the free face in the direction perpendicular to the tunnel axes; the stress first assembles, then decreases suddenly close to zero and finally increases to a certain value as observed profile is firstly close to and then far away from the tunnel face. The laws above mentioned are different from those obtained from middle and low stress environment. Knowing these laws, characteristic and mechanism of stress redistribution is useful for design, construction and support of the tunnel in order to prevent disaster.
The financial supports from National Natural Science Foundation of China under grant no. 50909092, the Special Funds for Major State Basic Research Project under grant no. 2010CB732006 and Natural Science Foundation of Hubei Province under grant no. 2009CDB120 are gratefully acknowledged. The authors would like to give their acknowledgement to Senior Engineerer Errol de Kock for his helpful suggestions to improve the manuscript.