Optimization Research On Thickness Of Middle-wall And Support Parameters In Large Cross-section Arch Tunnel

Large cross-section arch tunnel is a newly arisen tunnel form which is different from normal arch tunnel. Middle-wall is a important component of arch tunnel. The thickness of middle-wall is a very important parameter related to the global stability and engineering cost of tunnel, and so as the support parameters. There are many problems about the arch tunnels under construction and in built at present, such as, too strong in general supporting system, weaker in partial position, cracking and leakage on the lining and cost too much at shallow section and higher level surrounding rock section. It is very necessary to optimize the thickness of middle-wall and support parameters of arch tunnel. This paper studied these problems mentioned above depended on Hukeng Tunnel which is a six lane and two holes arch tunnel under construction between Sihui and Huaiji on Guanghe Expressway.â‘ The engineering geological condition and hydrogeology condition of Hukeng tunnel, classification of surrounding rock and so forth of the section design, support structure design and construction method are systematically introduced in the paper.â‘¡The purpose and basic requirements of multi-arch road tunnel monitoring measurement and so forth of the monitoring items and section arrangement of Hukeng tunnel are briefly introduced in this paper. The monitoring information in middle pilot heading of Hukeng Tunnel at V class surrounding rock section is analyzed and evaluated after that.â‘¢The basic principle of underground engineering analysis using Finite Element Method is elaborated. By using the large universal finite element software ADINA, construction process with large deformation nonlinear finite element method simulation analysis is made under the condition of V class surrounding rock when the thickness of the curved middle-wall is 2.2 m (design value) and 1.34 m (optimal value). Comparison is also made between the simulation results and the monitoring results of middle pilot tunnel. The results show that the simulation results and monitoring results of middle pilot tunnel is basically identical. The constitutive model and physical mechanical parameters of surrounding rock used by finite element simulation is comparatively reasonable. The results also show that there is no obvious advantage when the thickness of the curved middle-wall is 2.2 m in extreme stress and displacement of surrounding rock, supporting structure and curved middle-wall, extreme axial force of bolt, and so forth of key part stress and displacement of surrounding rock and supporting structure. There are some advantages when the thickness of the curved middle-wall is 2.2 m in key part stress and displacement of the curved middle-wall, but the advantages are not obvious. It is feasible to determine the thickness of the curved middle-wall to 1.34 m.â‘£On the base of middle-wall thickness optimization, the parameters of supporting structure are optimized under the condition of V class surrounding rock. The result shows that there are some and not so obvious advantages of the original designed supporting parameters in extreme stress and displacement of surrounding rock, curved middle-wall, key part stress and displacement of surrounding rock, curved middle-wall. There are more advantages of the original designed supporting parameters in extreme stress and displacement of supporting structure, key part stress and displacement of supporting structure, especially in extreme axial force of bolt. Assisting construction measures and monitoring of bolt should be taken when using this optimization scheme. The optimized support parameters is basically feasible on the condition of strengthening assisting construction measures and supporting on weak part, though the original designed support parameters are more advantageous.