Study On The Longitudinal Seismic Performance Of Box Tunnel Effected By The Spacing Of Seismic Joint

In recent years, China’s urban traffic is becoming more and more crowded, which has brought a great inconvenience to the residents, but also restricted the development of urban economy. In order to ease the traffic pressure, China is vigorously developing three-dimensional transportation network. Developing the urban underground road is an effective measure to shunt the ground vehicle, and is also the future development trend of three-dimensional transport. However, China is regularly shaken by earthquakes, and is lack of experience in seismic design of the urban underground highway tunnel, so it is urgent to carry out the related research. Based on the above background, the main research work in this paper is as follows:This paper introduced the theory of seismic deformation method and its application in the analysis of tunnel longitudinal seismic response, explored the detailed method of solving the foundation’s spring stiffness and time history waveform of displacement, and also discussed the relationship in theory between the stiffness and the seismic performance of tunnel. This paper summarized the general process of tunnel seismic design, taking a Japanese underground highway tunnel as the research object, described in detail the specific process of setting up the finite element model and solving the relevant parameters, then introduced the principle and method of setting up the seismic joint in the initial scheme. After the analysis of TDAP3 software, specific locations of internal force and joint’s deformation that exceed the allowable value were found out, and the space of seismic joint could be adjusted pertinently. Analysed the calculation result of the adjustment scheme and compared with the initial scheme, then obtained the influence of seismic joint space on seismic response of box tunnel by using the flexible connection.Through the analysis of the research, the following conclusions can be concluded:Tunnels are prone to damage seriously in these parts: the section change position—just like the intersection or bifurcation position, small radius curve position, stiffness mutating position etc. There are usually internal force mutation and deformation mutation in these special positions, so this situation requires special attention in the design. The position that is prone to damage seriously should be setted up the seismic joint, and the adjacent sections of these parts should also be setted up several seismic joint to share the possible larger internal force and deformation(10m~15m or so). Small radius curve section should be setted up the seismic joint with the smaller space(10m or so). It is not recommended to increase seismic joint space blindly in the straight tunnel section(the maximum is about 45 m and large values are not allowed to be used continuously), otherwise there will be internal force mutation or deformation mutation at a certain position. Seismic joint space should be adjusted from big to small gradually to find the reasonable value, otherwise it will be difficult to find a basis and adjustment will lose the pertinence. Reducing the seismic joint space can eliminate the mutation "point of point" of internal force and deformation. Using the flexible joint with constrainting function can effectively release the seismic stress and inhibit the deformation of seismic joint, to avoid the contradiction between internal force’s decrease and deformation’s increase after reducing the seismic joint space.The theoretical method and special structural measures have been widely used in engineering practice in Japan, so it’s highly feasible, the conclusion of the research can improve the maturity of tunnel’s seismic design in China; research conclusions on the principle of setting seismic joints and adjusting the space of seismic joint can provide a clear working direction for engineers, but also can greatly reduce the workload of setting reasonable seismic joint spaces.