Existing Subway Shield Tunnel Stability In The Upper Part Of The Pit Excavation

At present mechanism of the study that Excavation is bound to affect the stress and deformation of the shield tunnel below it is less, and the analysis theory is still not perfect. Therefore, it has the quite important theoretical and practical reference value that further analysis of the specific research. Taking a shield tunnel in the upper pit excavation stability in the process of the research as a starting point, and fiber Bragg grating sensor technology to monitor the vertical deformation of wuhan subway 2 in the process of excavation for background, and the finite element analysis method to analyze the research, and at the same time, with the finite element numerical simulation results and the measured data analysis contrast, the main research contents and conclusions are:(1) Analyzes the subway shield in upper under the action of foundation pit deformation mechanism, tunnel to vertical deformation is given priority to, basic can ignore level with the direction of the axial deformation, and introduces the vertical tunnel deformation characteristics of the tunnel and soil in the role of the calculation model.(2) Research and develop distributed settlement tube that based on optical fiber grating sensing technology, makes the installation of the tube tunnel segment distributed settlement with perception, realize the real-time monitoring of the tunnel settlement, thus of tunnel excavation course in upper the deformation mechanism.(3) Useing distributed settlement tube to monitor Wuhan metro line 2 a, the data show that happened after the first tunnel settlement prices of phenomenon. Through analysis and study, before foundation pit excavation, tunnel counterweight and precipitation caused the settlement of tunnel in the soil, after the excavation unloading, just appear the prices of phenomenon.(4) According to the geological data and the surrounding environment, using ABAQUS finite element software based on the finite element numerical model to verify the fiber Bragg grating sensor technologies to measure the accuracy of the tunnel settlement, and get the tunnel excavation course in the upper the deformation law.(5) The finite element analysis and the actual data contrast analysis showed that, in the whole process of foundation pit excavation, numerical simulation and measured results show that the vertical displacement of the tunnel laws are consistent, also reflect the finite element method is applied to the study of shield tunnel in the process of foundation pit excavation in the vertical deformation law is feasible, but also prove the fiber Bragg grating sensor technology can be applied in the subway to monitor the settlement of shield tunnel.