Research On Vertical Deformation Of Existing Underlying Subway Tunnel Caused By Symmetric Excavation Of Two Deep Foundation Pits In Soft Soil Area

With the rapid development of economy, there has been a mushrooming of metro construction in big cities. Subway tunnels often pass through the down town area of the city. So more and more deep foundation pit adjacent to the subway station and the subway tunnel. The interaction between the deep excavation and the subway is becoming more and more serious. Forecasting correctly the tunnel deformation caused by deep excavation, which has important guiding significance for the safety construction of deep foundation pit and the safety operation of the subway.At present, there is insufficient appreciation about the effects of excavations on existing underground tunnels in soft soil area. The deformation of metro tunnel caused by near deep excavation is hot issue in the underground transportation construction safety control and risk assessment. Therefore, intensive study of the connection is necessary for theory and application. Firstly, the dissertation summarized the calculation method of upheaval in the bottom of the deep excavation. Then the simplified calculation formula of the additional stress of tunnel represented by Hangzhou is deduced. At last, the numerical analysis method and the field test method are used to study the deformation of existing tunnel caused by deep foundation pit in soft soil area. The main work and results of this paper are as follows:(1) By consulting the literature, summarize the research methods of excavation impact on subway tunnel. These methods includes:empirical prediction method, theoretical analysis, model test, field test and numerical analysis method.(2) The theoretical calculations model for excavation impact on subway tunnel is derived. According to Mindlin solution of elasticity theory and considering the nonlinear rheology of soft soil, the simplified calculation formula of the additional stress of tunnel is deduced.(3) By analyzing the models, Mohr-Coulomb is used to simulate the soil. And the parameters of each soil layer in the numerical simulation are determined.(4) The software of FLAC3D is used simulate the project. Simulated results show that deep excavation has a greater effect on the horizontal displacement of the subway station and has a smaller effect on the vertical deformation of the interval tunnel. The deformation of subway station and tunnel is within the allowable range by taking symmetrical excavation and pre reinforcement method of subway station(5) Based on the field test, the validity of the numerical simulation is verified by comparing between the measured results and numerical simulation results. The time effect of the construction can not be considered because of the instantaneous deformation in numerical simulation. So the numerical results can be used only for qualitative analysis.Finally, some valuable construction experiences are summed up. These results can be a good reference for the similar engineering.