Nonlinear Dynamic Responses Of Tunnels Under Longitudinal Seismic Actions

Shield tunnel structure contains a large number of connecting bolts, which is an important factor leading to the flexible characteristics. The deformation of the soil around the shield tunnel can induce structure movement, while the structure movement is constrained by the surrounding environment. So there are some certain response characteristics in shield tunnel when the earthquake occurred.The second and third chapters are devoted to study the vibration characteristics of shield tunnel under the longitudinal earthquake. At first, the soil-structure interaction was modeled by springs with equivalent stiffness, and the motion equations of structure under seismic action were derived.Central difference method was used to solve the obtained motion equations and the displacement of every section at different moment of time was obtained. Furthermore, the effect of three parameters, including soil-structure shear coefficient, seismic P-wave velocity and structural connection stiffness, on shield tunnel segment displacement was investigated.The numerical results show that, as the soil-structure shear coefficient increases, the maximum displacement of tunnel segment would increase, and the relative displacement between the structures reduces. After reducing the stiffness of the structure, the relative displacement between the structures and the soil reduces. The lower the wave propagation speed, the larger the relative displacement between the structure and formation becomes, which leads to the slip phenomenon.The nonlinear interaction of the soil and the structure on the tunnel seismic is studied in the fourth chapter. Through analyzing the pipe segment displacements and comparing the size of them under the condition of the nonlinear interaction between the soil-structure of the dynamic response characteristics, it is concluded that when constraints of soil-structure is less, the relative displacement of the segment and the soil becomes lager, so as the relative displacement of adjacent segments, which is showed that the displacement of soil and structure is lager under the strong earthquake and the interaction effect of the soil-structure is no longer in linear state. If the usage of the spring linear stiffness taking place of the relation of soil-structure effects is still in use, the accuracy of the engineering calculation can not be guaranteed.According to research results, the fifth chapter presents some of the seismic damping measures to improve the seismic structure performance, such as selecting hard ground with a faster velocity, increasing the shear forces between soil and structure, and setting a reasonable distance of the seismic joints.