Field Test Optimization of Shield Tunnelling Parameters Undercrossing an Existing High-Speed Railway Tunnel: A Case Study

An existing high-speed railway tunnel undercrossed by shield tunnelling is a high-risk project. Selecting reasonable shield tunnelling parameters is key in controlling the deformation of existing high-speed railway tunnels. In this paper, a Metro Line 3 undercross of an existing high-speed railway tunnel project is taken as the research background. First, a shield section with similar geological conditions as the undercross section is selected as the test section. Then, reasonable shield tunnelling parameters are determined by monitoring the settlement values of surface and ground structures in the test section. Finally, combined with the monitoring results of vertical soil displacement, the reliability of the shield tunnelling parameters is verified. After the completion of shield tunnelling in the test section, there is no void behind the shield tunnel wall, and the monitoring results of the vault settlement and segment posture in the tunnel meet the control values in the specification, which further support the rationality of the tunnelling parameters. In the process of shield tunnelling the undercross of the existing high-speed railway tunnel, the monitoring results of overall tunnel settlement, bottom uplift point settlement, track settlement, and track height difference meet the control values in the specification, which effectively avoids the adverse impacts of the shield tunnelling undercross of the existing high-speed railway tunnel and ensures the safety of the existing tunnel.