Analysis of Unloading on Underlying Shield Tunnel Based on Equivalent Beam-Hinge Joint Model

There are many engineering cases of excavation of foundation pit above subway tunnel in domestic cities. As the extremely strict deformation control for subway tunnels, it is necessary to accurately evaluate the influence of unloading and the corresponding deformation control measures. Numerical simulation analysis of prefabricated shield tunnel is carried out, considering the influence of the segment joint, the tunnel segment is equivalent to the beam-hinge joint model. The ground-structure method is used to establish the overall model, and the HSS model is used to analyze the influence in excavation cases on the vertical uplift and radial convergence deformation of the underlying shield tunnel. Further the effect of deformation control is analyzed under tunnel protection measures. Combined with the engineering example, the research shows that the equivalent beam-hinge joint model can simulate the radial convergence deformation of shield tunnel and obtain the deformation attitude of “vertical duck egg”. With the tunnel deformation control measures, the tunnel uplift can be controlled within 1.5 ‰ times the excavation depth. The research results can provide guidance for the monitoring and control of operating shield tunnels.