Study On Excavation Stability Of Slurry Shield Tunnel In Hejiang River Under High Water Pressure Condition In Hengyang

Shield tunneling method has less environmental impact on the surrounding environment,and does not affect normal shipping,construction is not affected by season,weather and other climatic conditions,and does not produce noise in the process of shield tunneling.Shield tunneling method has become the main method of urban tunnel construction.However,with the construction environment of shield tunnel becoming more and more complex,there are many problems in the construction process,especially in the cross-river tunnel project.Because of shallow soil cover and large water pressure,the stability of tunnel excavation face is difficult to control.A little carelessness will lead to river water backfilling,excavation surface collapse and other accidents.In this paper,the stability of slurry shield under high water pressure is studied by theoretical analysis,numerical modeling and on-site monitoring combined with the Hejiangtao River-crossing Tunnel Project in Hengyang.(1)Based on the theoretical study of mud film formation law at home and abroad,a mud membrane layered infiltration model was constructed.The mud film thickness,filtration loss and time were calculated by using MATLAB program.The validity of the model was verified by comparing with the traditional cake filtration theory.(2)Based on the theory of limit equilibrium analysis,combined with wedge model and unified parameters of soil and water,the theoretical calculation model of limit support force of excavation face under high water pressure is established.(3)Flac3d is used to calculate the limit value of support pressure on the excavation face of slurry shield tunnel under high water pressure.The influence of internal friction angle,cohesion,tunnel depth and tunnel diameter on the support force of excavation face is analyzed,as well as the change rule of failure mode when the tunnel is unstable.(4)Combined with the Hejiang Tunnel Project in Hengyang,a typical section of the project is selected for stability analysis,and the theoretical calculation model,numerical calculation model and support force used in actual construction are compared to evaluate the actual construction safety.