The Process Simulation Of Subway Tunnel Construction And The Analysis Of The Ground Surface Subsidence

Large-scale constructions of subway extract many problems while offering conveniences for people. The excavation of metro tunnel can cause the subsidence and crack of the ground, as while as the sink of surrounding buildings foundation, in severe cases, it can lead to the road or buildings collapse. So, in order to ensure the safety of metro construction, we should understand the regulation of the ground settlement caused by construction. This paper is written depend on the engineering case of Dalian Metro2, building block205.Through the use of Mixed Used Theory, On-site monitoring data analysis and software FLAC3D, it makes analysis for the ground settlement and the discipline of ground settlement caused by the overlapped shallow single tunnels of Dalian Metro. At the same time, it utilizes software FLAC3D to simulation the excavation conversation by Method of Up and Down the Steps. Below are the conclusions:First of all, the paper expounds the theory of shallow burying and subsurface excavation method, emphatically analyzes the surface subsidence deformation mechanism and the main reason of ground surface subsidence, and represent some prediction methods of the surface subsidence.Secondly, combine the bid205shallow tunnel in dalian subway tunnel engineering construction process, survey the surface subsidence of the tunnel, tunnel construction process were studied, and the regulation of the ground surface subsidence. Analysis the data, summary the regulation, and get the following conclusion:all the settlement trends of measuring points are proved to be double exponential curve. Settlement is mainly formed in the sharp subsidence stage. That is because surface subsidence deformation rate suddenly become larger which accounts for about85%of total settlement, When the measuring point away from the excavation working face is distancing between the negative1.25times of cavity diameter to the3cavity diameter range.Again, through the research and analysis of the data on the spot, combined with FLAC3D numerical simulation, has found that:with the increasing thickness of tunnel vault covering, corresponding cumulative subsidence of surface get smaller and smaller, but the corresponding surface settlement trough width increases; with the thickness of overlying soil increasing, the percentage between the actual measurement of vault settlement and the maximum value of the cumulative surface settlement will get bigger, the scope of the percentage is about50%～70%. Finally, based on numerical simulation analysis, in the method of the up and down steps during the construction, the maximum ground surface settlement caused by the excavation of the upper section accounts for roughly71.43%of the maximum accumulative settlement of surface in the process of construction; the second half of the cross section accounts for28.57%.