Large Diameter Shed-pipe Advanced Support Effect And Parameters Optimization Analysis In Tunnel Construction Projects Undercrossing Existing Metro

With the continuous development of the urban metro and high-speed railway network, a large number of crossing metro projects emerge inevitably in range of the metro control protection. For new crossing engineering projects especially those crossing under the existing tunnels with track structure, the construction will cause the soil disturbance in surrounding rock, and lead to vertical and horizontal deformation of track structure, resulting in track additional irregularity. On the other hand, with a large number of the construction of metro and high-speed railway currently, the importance of tunnels is increasingly prominent in traffic. To ensure safety and rapid construction of tunnels, the advance pre-supporting is usually needed, wherein the shed-pipe advanced support system has been widely used. The rationalization of shed-pipe advanced support system design parameters determines the safety of entire project construction, ground deformation and effect the operation of the existing line. Therefore, it is necessary to do research about supporting result of pipe shed in the tunnel, which has important theoretical and practical value for ensuring comfort and safety of trains during the construction.The paper deals with large diameter shed-pipe advanced support effect and parameters optimization analysis in tunnel construction projects undercrossing existing metro, the main research contents and results are as follows:(1) Choose two typical examples about crossing engineering projects with shed-pipe advanced support. With finite element analysis software ANSYS, the deformation of existing railway track caused by the construction of shed-pipe and pilot tunnel is analyzed and shed-pipe advanced support effect is discussed. Calculation results show that the combination of shed-pipe and grouting can greatly reduce the vertical deformation of the track structure caused by new project construction. Meanwhile, it is observed that vertical deformation of the track structure caused by shed-pipe construction is half of that by whole construction. Shed-pipe support effect appeared gradually along with each pilot tunnel excavation and result in effective control of the track structure deformation caused by tunnel construction process.(2) Based on the practical project, build2D models with finite element analysis software ANSYS to analyze the influence of shed-pipe supporting effect by different design parameters. With reasonable design parameters of shed-pipe can minimize the shed-pipe construction influence impacted on the railway, but the width of the settlement trough is approximately the same. The deeper the new tunnel buried, the smaller influence is made on track structure caused by shed-pipe and pilot tunnel construction. But proportion about vertical deformation of the track structure caused by shed-pipe construction to that by whole construction basically has nothing to do with depth of new tunnel.(3) Based on the practical project, establish vehicle-track spatial coupling dynamic model with SIMPACK to analyze vehicle dynamic performance about safety and comfort. Tunnel-construction causes adverse effect on vehicle running safety comfort. But it can be deduced to a certain extent with original speed by adopting reasonable design parameters of shed-pipe roof support system.