Abstract: 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 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).

Key words: super-large span highway tunnel, construction method, support parameters, mechanized construction