| In the process of rapid development of urban construction in China,underground lifeline projects such as electric power tunnels are being constructed in full swing.Limited by the urban land,new tunnels often cross the relationship with existing underground engineering,resulting in tunnel cross crossing and underpass existing tunnel close construction,which causes disturbance to the soil mass and causes the surface deformation settlement.Therefore,the impact of shield tunneling on surface deformation and the risk assessment of surface deformation during shield tunneling have always been the focus of research in related fields.This paper takes the shield tunneling under an existing rectangular power tunnel section of a certain project in Beijing as the research object.Based on the numerical simulation,a three-dimensional model of the shield tunneling under the existing rectangular power tunnel is established to explore the influence of different factors on the surface settlement deformation,and a comprehensive assessment of the risk of surface deformation caused by the shield tunneling under the existing rectangular power tunnel is carried out by combining qualitative and quantitative methods.This study can reduce the influence of shield tunneling on surface deformation,and provide theoretical and technical support for surface settlement control and similar engineering.The main content of this study is as follows:(1)Based on the engineering geological data,the topographic landform,geological structure and lithology of the supporting project are analyzed,the mechanical process of shield tunneling construction is summarized,and the mutual influence principle of shield tunneling,existing rectangular tunnel and overlying soil layer is revealed during construction.The influencing factors of shield tunneling on ground deformation are analyzed,and the main parameters affecting shield tunneling construction are classified and analyzed.(2)Based on the numerical simulation,a coupling three-dimensional model of "shield-rectangular existing tunnel-soil" was established to carry out dynamic numerical simulation of the construction of the shield tunneling under the existing rectangular power tunnel,and to analyze the influence of the construction process on the formation,surface deformation and the deformation of the existing rectangular tunnel.The results show that the influence of underpass construction on the existing rectangular tunnel and ground deformation is mainly in the 3-fold diameter range centered on the crossing point.The existing rectangular tunnel presents the characteristics of vertical displacement "first rise and then sink",horizontal displacement "slow forward-fast forward-slow forward" and slight torsional deformation.(3)The impact of net distance was analyzed during the research process,which mainly utilized orthogonal simulation methods,cross Angle and water level change of the new and old tunnels on the surface and the existing rectangular power tunnel in the construction of shield tunneling.The results show that the surface settlement increases first and then decreases with the increase of the net distance between the new and old tunnels.The surface settlement decreases with the increase of the Angle between the two tunnels.The surface settlement increases with the increase of water level.(4)Determine 19 risk factors such as tunnel diameter and net distance between two tunnels,establish risk probability evaluation indexes of shield tunneling construction and determine corresponding prior probability values;The risk probability network model of tunnel design parameters and soil profiles is established by Bayesian network method.A risk assessment method for shield tunneling under the existing rectangular power tunnel is proposed,and a comprehensive risk evaluation is carried out.The results show that the construction risk probability is 0.747,which is a "relatively dangerous" risk probability level. |
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