Environmental Impact And Risk Assessment Of Double Shield Tunnel Oblique Crossing Railway Frame Bridge

With the continuous development of economy and society,surface transportation has been insufficient,and the development of underground rail transit is growing rapidly.Shield construction is an important construction method of subway tunnel.During the construction process,the surrounding soil will inevitably be disturbed,resulting in stratum deformation and affecting adjacent roads,buildings,bridges,etc.Based on the research background of Changsha Metro line 3 shield double tunnel oblique crossing the frame bridge of Beijing Guangzhou railway,this paper studies the environmental impact and control technology of shield double tunnel oblique crossing the frame bridge.The main research contents are as follows:(1)In the process of shield construction,by arranging settlement monitoring points on the surface and frame bridge,the surface settlement monitoring results are analyzed,and the law of surface deformation in different excavation stages of double shield structure excavation is summarized.The monitoring results of frame bridge settlement are analyzed,and the deformation law of frame bridge in different stages of shield excavation is discussed.(2)Using the numerical simulation finite element software Midas GTS NX,selecting the appropriate model,and based on the stratum physical and mechanical indexes of the study area,the numerical simulation analysis of the double shield oblique crossing railway frame bridge is carried out,and the obtained numerical simulation results are compared with the monitoring results.(3)Based on Peck theory,the surface settlement caused by shield excavation on the right line and left line is predicted,and compared with the measured data and numerical simulation,the prediction model of surface settlement caused by double line shield excavation is constructed,and the reliability of the model is verified.Based on Winkler theory and considering the uneven settlement of frame bridge in each section in the whole process of shield excavation,a practical calculation method of the impact of shield excavation on the upper existing frame bridge is established,which provides a reference for the prediction of uneven settlement of frame bridge in similar projects.(4)In order to ensure the safety of shield construction and analyze the impact of various factors on shield construction,based on entropy weight method and cloud model theory,a safety risk assessment model for shield tunnel crossing frame bridge construction is established,and the safety risk assessment of shield tunnel crossing frame bridge project is carried out.The research shows that the overall risk of the shield tunnel oblique crossing railway frame bridge project is level II,which is tolerable and needs to be paid attention to.The risk assessment level of environmental impact factors of the project is level III,which is an acceptable risk and needs to be considered.Specifically,it needs to focus on the uneven settlement of frame bridge and surface settlement.