Construction Mechanics Security Analysis Of Large-Span Shallow-Buried Excavation Tunnel Of Metro

With the rapid development of cities rail traffic, in the plan and construction of China's urban rail transportation network, the demand of large-span shallow-buried excavation tunnels are more and more. Compared with the tunnels constructed before, the construction of shallow-buried large-span excavation tunnel has put forward many new requests in aspects of the tunnel excavation methods, supporting mode and parameters, mechanical behavior of tunnel, thus the construction technique of shallow-buried of large-span tunnel needs to further perfect and improve.In this paper, the main research objects are the shallow-buried excavation of large-span,multi-sectional tunnels of Beijing Metro Line 10th Garden Road Station～Badaling high-speed station interval, simulates the dynamic excavation process of large-span shallow-buried excavation tunnels in weak geology by finite element analysis software ANSYS, analyzes the construction security of large-span tunnels excavated in different modes, as well as the mechanical state of construction method conversion between different sections through the numerical simulation. The main contents for researching are as follows:1, The interaction mode of formation and structure of the elastic-plastic three-dimensional FEM is adopted in calculation, the 3D-FEM analysis is carried by FEM software ANSYS. Through the mechanical analysis of large-span shallow-buried excavation tunnel, researches the development of tunnel deformation, mechanical law, as well as surface subsidence caused by construction with middle hole excavation method and two side hole excavation method, and find the key to control of the subsidence.2, The construction of sections conversion is one of the difficulties of tunnel excavation, in order to ensure transition in security, in the construction must to be closely the basic principles of shallow-buried subsurface excavation method, according to the interrelationship between sections and the use of engineering methods, make full use of advanced support measures to reinforce the surround rock, realize section conversion by using grid hanging iron net of shotcrete support. Mutation sections construction conversion calculation mainly research the small tunnel section to the large section tunnel conversion process, the surrounding rock stress change under different support conditions, find the key technology of section conversion construction.Finally, the main conclusions, the problems and the technical innovations are expounded and some own opinions are proposed in the paper.