Analysis Of Longitudinal Seismic Of Shield Tunnel With Longitudinal Equivalent Continuous Model

Shield tunnel is one of the important lifeline engineering, so the research on its seismic security has the important social, politics and economic significance. With the accumulation of seismic disaster data and the development of scientific research, people have gradually realized the deficiency of pseudo-static mechanics method when analyzing the seismic response of underground structure. On the other hand, the seismic deformation method and the dynamic finite element method is considered to be preferable.This article adopt beam element to simulate the characteristics of the shield tunnel, establish longitudinal equivalent continuous model of the shield tunnel, get the equivalent tensile stiffness and the equivalent bending stiffness through the theoretical analysis and calculation, and expound the calculation principle and method steps of the seismic deformation method and the dynamic FEM.The shield tunnel constructed on the soft soil layer in Tianjin city is used as an example to get the maximal axial compression/extension force and longitudinal bending moment of the tunnel in the condition of the Sinusoidal Displacement Travelling-Wave at 0 degrees and 45 degrees incident and can be calculated as well as the force and displacement of the blots and the concrete by adopting the seismic deformation method and the dynamic FEM and considering both the seismic intensity 7 (PGV =0.15m/s) situation and seismic intensity 8 (PGV =0.30m/s) situation.Besides, by analyzing the imputing ground motions, bolt strength, Segment size and tunnel diameter,these article put forward some suggestions which are suitable for the designs of longitudinal seismic of shield tunnel.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 in strong earthquake. Then nonlinear dynamic FEM have to be adopted.5. 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.