Study On Longitudinal Seismic Mechanical Model Of Shield Tunnel And Its Application

Shield tunnel is an important component and main structure of modern urban underground rail transit,so it has important social and economic value to study the safety performance of shield tunnel.China is a country with high incidence of earthquakes.Earthquakes have an important impact on the safety performance of shield tunnels.The internal forces generated by earthquakes in the longitudinal direction of shield tunnels are very complex,which will produce both longitudinal axial forces and bending moments in the structure.However,the study on the coupling effect of axial forces and bending moments has not been in-depth.In this paper,the longitudinal seismic response characteristics of shield tunnels in uniform strata are studied.Based on the longitudinal equivalent continuous model of shield tunnels proposed by Shiba,a longitudinal deformation model of shield tunnels is proposed,which can simultaneously consider the coupling effect of longitudinal axial forces and bending moments.Based on this longitudinal deformation model and seismic deformation method,an iterative calculation method considering equivalent stiffness updating is proposed,and the longitudinal seismic characteristics of shield tunnels are analyzed.Finally,the finite element method is used to validate the iterative calculation method.The main work and achievements in this paper are as follows:(1)Based on the longitudinal equivalent continuous model,the longitudinal deformation model of shield tunnel is established,which can analyze the coupling effect of axial force and bending moment.According to the deformation state of structure and the elastic-plastic properties of material,the model is divided into five deformation modes.For each mode,the expressions of longitudinal equivalent bending stiffness,equivalent tension-compression stiffness,structural deformation and internal force are obtained by analytical calculation.(2)The prestressing force,the strength of bolts and the diameter of tunnels have important effects on the equivalent stiffness of the structure,which need to be considered reasonably in practical engineering.(3)Based on the seismic deformation method and the longitudinal deformation model of shield tunnel proposed in this study,a longitudinal seismic calculation method of shield tunnel is proposed.The method use iterative calculation to update the structural stiffness.The internal force and deformation of shield tunnel structure under the coupling of longitudinal axial force and bending moment caused by earthquake can be solved by this method.(4)Based on the iteration method proposed in this paper,the most unfavorable incident angle of seismic shear wave is calculated.According to the opening of joints,the most unfavorable incident angle of seismic shear wave is determined to be 45°.