Study On The Influence Of Shield Tunneling Through Existing Subway Tunnels In Water-Rich Silty Clay

Taking the section of Zhengzhou Metro Line 10 from Medical College Station to Zhengzhou Railway Station as the engineering background,the influence of shield tunneling in water-rich silty clay in Zhengzhou area on the existing subway tunnel is studied.Through the numerical simulation analysis of no settlement control measures and three different settlement control measures,the law of settlement deformation of the surface and the existing subway tunnel during shield tunneling is studied,the settlement control measures of the surface and the existing subway tunnel are proposed,and the shield construction parameters are determined.The numerical simulation data are compared with the actual monitoring data.The main research results are as follows :(1)Considering the hydrogeological conditions of the project,the previous research results,the current situation of the existing subway tunnel structure,the relevant specifications of the domestic industry,the safety impact grade of the project and the settlement deformation control standard is determined,and the shield machine is selected.It is found that the earth pressure balance shield machine is more suitable for the water-rich silty clay in Zhengzhou area.Combined with the monitoring data of the project site test section,the main construction parameters of this shield tunneling project are determined.(2)Through the numerical simulation of the whole process of shield tunneling,it is found that when the new left and right tunnels are completed,the surface will appear as a Ushaped settlement trough;the existing subway tunnel has isolation effect on soil disturbance caused by shield tunneling,so the surface settlement trough above the existing subway tunnel is shallower than that at other positions.(3)By analyzing the numerical simulation results,it is found that the settlement curve of the existing subway tunnel is V-shaped and the settlement area is above the new right line tunnel when the new right line tunnel passes through the existing subway tunnel.When the new left-line tunnel is also completed,the settlement curve of the existing subway tunnel will also appear V-shaped above the new left-line tunnel.The settlement curve of the existing subway tunnel will show a W shape as a whole.(4)From the results of numerical simulation analysis,it can be seen that when the two settlement control measures of the front and middle end of the shield grouting reinforcement and the longitudinal reinforcement of the existing subway tunnel segment groove steel are adopted at the same time,the settlement value of the surface and the existing subway tunnel can meet the control standard requirements of this project.(5)By comparing the actual monitoring data and numerical simulation data in the construction process,the accuracy of the numerical simulation and the adaptability of the Mohr-Coulomb model in the water-rich silty clay layer are verified.It also proves the effectiveness of two settlement control measures,i.e.,the grouting reinforcement with clay effect at the front and middle ends of shield tunnel and the longitudinal tie reinforcement of existing metro tunnel segment slot steel.