Control Measures of Shield Tunnel Overlapped in Soft-flow Plastic Formation

In order to analyze the control measures of tunnel excessive settlement and sudden instability in the process of shield overlapping construction in soft flow plastic stratum. Based on the project of Nanjing Metro Line 5 Sanshanjie Station Chaotiangong Station Section Tunnel Overlay Line 1, we use the numerical simulation method, based on the difficulties of shield construction in soft flow plastic strata and the mechanism of the impact of shield overlapping construction on the surface and existing tunnels, according to the different control means and objects, the results are as follows.（1）Internal tensioning steel ring method+micro disturbance grouting in the tunnel+secondary grouting reinforcement;（2）Double-layer pipe shed+cement soil mixing pile+sleeve valve pipe grouting reinforcement;（3）The control effect of three pre reinforcement measures for MJS construction method reinforcement is compared and analyzed. The research results show that the maximum ground settlement values of the three control measures are 5.11 mm, 5.63 mm and 8.38 mm respectively, and the maximum settlement values of existing tunnels are 4.01 mm, 6.67 mm and 8.39 mm respectively. Scheme（1） could meet the settlement control values of overlapping projects. Finally, combined with the monitoring data of the best alternative shield overlapping construction site, the actual impact of the shield overlapping construction on the ground and the existing tunnel is further studied and analyzed, the control effect of the reinforcement measures is verified and analyzed, and the main settlement sections and effective control measures of the tunnel in the construction process are obtained, which provides a basis for such research and also provides a reference for the project construction.