A Large Span Tunnel Mechanical Response And Surface Subsidence Expected

With the rapid development of highways in China, there appear more and more constructions of large-span tunnel. Therefore, more and more problems existing in tunnel construction are coming out. For engineering technical personnel, how to choose suitable construction method has become an urgent problem that needs to resolve. The key is to study excavation and support processes for large-span tunnel and to obtain the information of mechanical character in terms of wall rock of large-span tunnel and supporting system when using different construction methods so as to provide basis and guidance for tunnel construction. Based on background Meiguan tunnel, the paper makes a research on three-dimensional numerical simulation for alternatives of different wall rock of tunnels and analyzes ground settlement induced by excavation of tunnel with shallow cover. The main content is as follows:(1) It sums up the distribution of rock stress of different sections in terms of ring tunnels, ellipse tunnels, rectangle tunnels and oval tunnels and analyzes the effect of the different flat rate, setting invert on the wall rock of tunnels;(2) It introduces tunnel stability factors, including the effect of gravitational stress, structural stress on the stability of wall rock of tunnels, and the research on Guangdong-Tunnel-rock types and stability with the help of artificial neural network;(3) It observes the tunnels, to which apply frequently used methods of New Austrian Tunneling Method, such as whole-section excavation method, steps-method, partial face excavation method, double-side-wall drift method and middle-wall method and so on.(4) It applies FLAC^3D to three-dimensional numerically simulating different construction plan on Tunnel of Guangdong entrance section of Meiguan tunnel, wall rocks section of grade IV and III respectively. In addition, the paper proposes reasonable construction plan with the help of comparative analysis of different simulations.(5) It comparatively analyzes the ground settlement from the aspects of values of stochastic medium theory and FLAC^3D numerical simulation and the measured, based on the underground excavating of Guangdong tunnel entrance section of Meiguan Tunnel so as to reveal the rules of ground settlement caused by excavating tunnel.