Deformation Law And Tunneling Parameters Optimization Of Shield Tunnel Crossing Underpass In Soft Ground

The shield method has become the primary choice for urban underground tunnel construction due to its small disturbance,controllable construction process,and fast driving speed.Disturbance and deformation of the shield construction on the surface is inevitable.Especially when passing through weak strata,if the construction parameters of the shield are not properly selected,it will lead to accidents such as excessive ground subsidence,surface collapse and damage to the ground structures,which endanger the safety of people’s lives and property.Studying the shield tunneling disturbance law,optimizing the shield construction parameters,and actively controlling the surface deformation is an important part of avoiding subway construction damage to urban municipal facilities and the safety of structures.In this paper,Fuzhou Metro Line 5project is the engineering research background,for the problem of long-distance parallel shield passing through the underground passage,the theoretical and numerical calculations are used to study the equivalent deformation parameters of the composite foundation reinforced by rotary jet piles.According to the shield structure and process characteristics,it is proposed the numerical simulation calculation method of shield tunneling disturbance effect is studied,and the shield construction parameters are studied and optimized.The main work of the thesis is as follows:(1)According to the working principle of the earth pressure balance shield,the mechanism of ground disturbance during shield construction is summarized and analyzed,and the different states of the stress on the excavation surface during shield excavation and the stage of surface settlement in the direction of shield advancement are explored Characteristics,stability control method of excavation face,and impact of excavation on upper stratum and surface.(2)Aiming at the problem of the value of the mechanical parameters of the composite foundation in the shield tunneling calculation model,based on the pile-soil stress transfer mechanism,a calculation method based on the equivalent deformation modulus of the composite foundation is proposed,which is different from the traditional area replacement method and elastic mechanics.Analytical methods and numerical analysis methods were compared;through numerical simulation of plate load test,the effect of pile group effect on the equivalent modulus of composite foundation was studied.(3)According to the principle of filling the shield process gap in the weak stratum to induce the deformation of the surrounding soil,a method to control the displacement around the tunnel to quantify the radial deformation of the shield tunnel is proposed.The engineering example is compared with the traditional stress relief method.verification.On this basis,the pile-soil solid element model and the composite stratum equivalent model were used to compare and analyze the spatial distribution of settlement deformation,and the PECK formula was used to fit the lateral settlement groove curve.(4)Through the analysis of three-dimensional shield tunneling,the relationship between the construction parameters and the maximum settlement of the ground during the tunneling process is studied,and the optimized shield tunneling construction parameters are proposed.