| In this paper we dissertate the FEM numerical simulation and the monitoring technology home and abroad in highway tunnel construction, then summarize the NATM in detail. In the consideration of shallow-depth, poor stability and complex geology condition of surrounding rock in the tunnel portal, we make studies by 2-D elastoplastic numerical simulation in tunnel portal construction. Based on the method of reversing and releasing the stress, we use plane strain model, then combined with the ANSYS program, we simulate continuous construction by load steps and tunnel excavation through "Birth" and "Death" method in the thought of releasing the stress step by step. After the analysis of displacement space and stress space of surrounding rock, we get the development regularity of stress and deformation during tunnel portal excavation by Bench Cut Method. Then we analyze the deformation and stability of surrounding rock in detail and get the development regularity according to time of ground surface settlement, vault crown settlement and horizontal convergence by using site monitoring data. On the basis of regression analysis we can make certain the surrounding rock stability and the optimum time for permanent support. In order to understand the deformation condition of surrounding rock in excavation process deeply, we make the numerical simulation results compared with the analysis results of in-situ testing data, then get some common regularities.At present, tunnel construction has a very important port in highway and railway construction, and the excavation construction in the tunnel portal is a key-link of tunnel construction. In this paper we make numerical simulation of tunnel portal construction on the basis of analysis in site monitoring results. It has important guide functions to the design and construction of tunnel obviously, and it can also be referred in the design, construction and research of similar tunnel in future. |
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