Abstract:Shield construction underpasses existing operating tunnels, which can easily lead to excessive deformation of existing lines and bring safety hazards to subway train operation. Considering the key factors such as the interaction between shield machine and soil, the interaction between lining?grouting layer and soil, and the synchronous grouting hardening process and pressure dissipation, a numerical simulation method for the whole process of shield construction is developed. Combined with the actual project, a three?dimensional finite element numerical model of shield tunneling under the existing tunnel is established. The structural deformation, internal force response, surrounding rock pressure and the development and change law of surrounding strata stress during the process of shield tunneling under the existing tunnel are obtained, and the deformation mechanism of the existing tunnel is revealed. The results show that the existing tunnel has flexural and torsional deformation in the longitudinal direction. The flexural deformation presents a ‘V’?shaped deformation with uplift at both ends of the middle settlement. The torsional deformation of the section is distributed in the form of large in the middle and small at both ends, and first reverses clockwise and then reverses clockwise with shield tunneling. For the tunnel cross section, the tunnel section presents the deformation mode of lateral flattening and vertical elongation in the range of x = ?0.8D to 0.8D, and the tunnel section presents the deformation mode of lateral elongation and vertical flattening outside x = ± 0.8D.In the range of x = ?0.8D to 0.8D, the deformation of tunnel section is caused by the unloading of soil caused by shield excavation, and the tunnel section outside x = ± 0.8D.
