Research On Longitudinal Nonlinear Dynamic Response Of Shield Tunnel And Its Seismic Design

Shield tunnel is one of the important lifeline engineering, so the research on its seismic security has the important social, politics and economic significance. In this dissertation, the problem of longitudinal seismic response and seismic design are considered. Field observations showed that there are two major causes to shield tunnel during ground shaking: earthquake wave propagation and differential subsidence due to earthquake. These aspects will be analyzed individually in this paper.In the research, the first and prime problem is how to model this specific discontinuous structure of shield tunnel, because shield tunnel is constructed with a lot of segments that are connected with the join bolts. In this dissertation, equivalent uniform model, which is advised by Japanese scholar, is adopted. Then shield tunnel is modeled as a uniform beam supported on the viscoelastic foundation of Winkler type. This model can avoid the problem that how to calculate the stiffness of longitudinal join bolts theoretically, which should be determined though model test. The nonlinear equivalent stiffness formula, considering the coactions of axial force and bending moment, is derived firstly. The nonlinear dynamic FEM program for analyzing the longitudinal response of shield tunnel subjected to earthquake wave propagation and differential subsidence due to earthquake. Stretch value of bolt is suggested as guideposts in design. Such aspects as equivalent rigidity, foundation parameter, domain and pattern of subsidence, reduced subgrade rigidity and non-linearity of bolt are discussed in detail. Some conclusions are obtained through analyses results.1. Longitudinal bolts always are weak links of shield tunnel. The aseismic design principle of substructure is how to adapt the deformation of circumference soil body.2. Maximal stretch value of bolt is suggested as guideposts in design, and plasticity ratio can favorably predominate plastic stress of bolts.3. It's necessary to considerate the axial force and bending moment coactions in the calculation of equivalent rigidity.4. In normal work condition, seismic deformation method is a simple practical method under traveling wave, but maximal stretch value of bolt will be too little instrong earthquake. Then nonlinear dynamic FEM have to be adopted.5. It's necessary to considerate the non-linearity of bolt in strong earthquake. High strength friction grip bolt and application of initial stress are propitious to enhance the earthquake resistance of shield tunnel.6. The thickness of segment should be lowest possibly, and increasing the width of segment-ring is unfavorable to enhance the earthquake resistance of shield tunnel. So it should be special approved.7. Such aspects of joint fashion, reduced subgrade rigidity, domain and pattern of subsidence is important to the earthquake resistance of shield tunnel. Some parameters have to be determined through special analyses in practice.Through the research on the longitudinal nonlinear dynamic response of shield tunnel due to earthquake, and the influence of some correlative parameters on the response, providing an academic foundation for seismic design code recension of shield tunnel and upgrading its seismic design. The methods and programs developed in this dissertation can also be used in analyzing the internal force of shield tunnel uneven ground settlement due to long-period load.