To rationally select construction methods and support parameters in the design and construction process of super-large span highway tunnels,a case study is conducted on a double-hole eight-lane super-large span highway tunnel of the Shenzhen-Shantou western expressway extension project in Guangdong province,China.The investigation,engineering analogies,and simulation calculations are employed to examine the construction method,supporting parameters,"one-hole nine-line"large-scale mechanized tooling configuration,and related optimization design of super-large span highway tunnel.Furthermore,the design scheme is validated through monitoring and measuring.The results reveal the following:(1)The design methods for two-and three-lane tunnels in the current specifications are still basically applicable to four-lane tunnels.(2)The center-diaphragm(CD)method is suitable for deep and strongly-weathered strata with a thickness in the arch no less than 1 times the excavation width of the tunnel;whereas the three-bench method is suitable for deep and moderately-weathered strata with a thickness in the arch no less than 1 times the excavation width of the tunnel.(3)The mechanized construction method can be applied in Grade Ⅳ surrounding rock after implementing ϕ51 advance middle pipe roof,glass fiber anchor,expanded shell prestressed anchor,and C30 early high-strength shotcrete.(4)Under the premise of advance pre-reinforcement and support optimization mentioned above,the mechanized construction method is applicable when the distance between the invert and the tunnel face is optimized to 106 m(CD method)or 118 m(three-bench method),and the distance between the secondary lining and the tunnel face is optimized to 160 m(CD method)or 190 m(three-bench method).
super-large span highway tunnelconstruction methodsupport parametersmechanized construction
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