Water inrush mechanism and minimum safe thickness of rock wall of karst tunnel face under blast excavation
LI Shu-cai1, YUAN Yong-cai1, LI Li-ping1, YE Zhi-hua2, ZHANG Qian-qing1, LEI Ting1
1. Research Center of Geotechnical and Structural Engineering, Shandong University, Jinan 250061, China; 2. Baoyi Expressway Construction Headquarters of Hubei Province, Yichang 444200, China
Abstract：The hydraulic fracturing of rock mass is one of the main factors for water inrush in karst tunnels. From the perspective of fracture mechanics, the impact of explosive stress wave on extension of water-carrying fracture is studied under drilling and blast construction. The results show that the expansion pattern of fracture is influenced by the pore water pressure produced by the explosive stress wave. By establishing the computational model for fractured rock mass, the critical water pressure (Pc) under the explosive stress wave is deduced, and it is verified by cases. Based on the theoretical analysis, numerical experiments and engineering cases, the hysteresis effect of water inrush caused by extended compression-shear failure of rock mass is obtained. According to the hysteresis effect, constructors can terminate construction and leave immediately before the occurrence of water inrush so as to ensure the safety of personnel and mechanical equipments. By analyzing the minimum safe thickness between the fractured rocks of karst tunnel face and high-pressure aquifer, “Two-band theory” is put forward. Furthermore, the formula for the minimum safe thickness is deduced, which can reflect the excavation and water pressure reasonably and is verified by engineering cases. It may provide a reference for the effective measures for water inrush in high-risk karst areas.
李术才, 袁永才, 李利平, 叶志华, 张乾青, 雷霆. 钻爆施工条件下岩溶隧道掌子面突水机制及最小安全厚度研究[J]. 岩土工程学报, 2015, 37(2): 313-320.
LI Shu-cai, YUAN Yong-cai, LI Li-ping, YE Zhi-hua, ZHANG Qian-qing, LEI Ting. Water inrush mechanism and minimum safe thickness of rock wall of karst tunnel face under blast excavation. Chinese J. Geot. Eng., 2015, 37(2): 313-320.
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