Single Arch Four-lane Highway Tunnel Cross-section Design Optimization And Construction Mechanics

The fast develop of economy cries for improving traffic carrying capacity. Usually, the width of road in tunnel narrows than the width of road out the tunnel, which is a throat to improve traffic carrying capacity. To build tunnel more lanes and bring a same width in and out tunnel is the way to solve it. The span-ratio of single-arch four-lane road tunnel is less than two or three lanes tunnel's greatly if technology and economic factors are taken into consider. Its surrounding rock and construction mechanic characteristics also different from two or three lanes tunnel's obviously, and the active code for design of road tunnel do not touch upon it too. Therefore, it is important to carry on the systematic research on the design and construction of the single-arch four-lane road tunnel.For geotechnical material's nonlinear characteristic, the calculating theory of large-span tunnel construction process is discussed. Then the mechanic response rules and stability of surrounding rock with difference span-ratio are analyzed. For optimum of single standard, the methods base on stress concentration factors, convergence around tunnel, plastic area and excavation area are introduced respective. As the major method of multi-standard optimum, Analytic Hierarchy Process (AHP) is employed, and then its rationale and steps are introduced. The inner section optimum process base on stress concentration factors, convergence around tunnel and excavation area is analyzed. The construction methods of large-span tunnel include basal and assistant construction methods and their class, serve range, advantage and disadvantage are also introduced. Meanwhile, the processes of whole section excavation method, two-side-gallery excavation method, benching tunneling method and middle-wall excavation method are simulated with finite difference program. And the surrounding rock and support mechanic response are analyzed in each. The methods are also compared with each other for selecting appropriate method to construct large-span tunnel. The relevant conclusions of this thesis can be referred by design and construct large-span tunnel.