| As the chief structure widely used in Traffic engineering and Hydraulic Engineering, the tunnel, which is designed well or not, affects the safety, economy and construction techniques of a project. Based on the present theory of tunnel design, this paper analyze the tunnel excavation process and research the optimal tunnel cross-section shape systematically via the elastoplastic finite element simulation analysis using the finite element analysis software ANSYS. And specific works are as follows:(1) Analyze tunnel construction process via the finite element numerical simulation. Combined with the nonlinear characteristic of geotechnical material, calculating theory of tunnel construction process and numerical simulation method are discussed. According to the finite element theory modeling, through confirming most of conditions, which are the design segment, physical and mechanical parameters, calculation range, boundary condition, element type, material constitutive relation, initial ground stress, the geometric model of tunnel is established.(2) Study the stability of different shape of rock sections. The finite element analysis software ANSYS is used to simulate the round, straight wall arch, egg-shaped and rectangular, four tunnel sections frequently used in current, in the same surrounding rocks. By analyzing the cavity stress, displacement, plastic zone, and lining loading situation, we can conclude that the egg-shaped is the reasonable cross sectional shape.(3) Research the mechanical properties of tunnel in different high-span ratio. On the meet to the limits of highway tunnels conditions, for five heart-round shell-shaped tunnel section, the stress distribution, convergence of vertical displacement and lining structure force conditions of the two-lane highway tunnel in the same tunnel width are calculated via numerical simulation, and the mechanical response, stability and variation of the lining force of the tunnel section could be achieved in different high-span ratio.(4) Study the multi-objective optimization of the tunnel section. The objectives of the tunnel section optimization are analyzed. Analytical Hierarchy Process (AHP) is employed in multi-objective optimization decision, and then its basic principle and calculation steps are introduced. By means of analyze and adjust the factors affecting the tunnel section, hierarchical relationship and stratum structure are established, and the algorithm procedures of Analytical Hierarchy are showed which applied to tunnel section in different aspect ratio. In the premise of meet to the tunnel structure gauge, as an indicator to the excavation area, around tunnel tension, lining internal force and convergence around tunnel, the optimal cross-section shape is selected.(5) Analyze the Mechanical of different Tunnel Construction excavation methods. Based on the optimal cross-section shape which is selected in before, the mechanical response of surrounding and supporting under different construction methods are analyzed, by simulating the construction process in the case of Grade III rock in full-face excavation method and step method. The reasonable program of excavation which provides reference for the tunnel design and construction is preferably obtained, through comparing and optimizing the two excavation methods. |
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