Dynamic Responses of Bridge–Tunnel Overlapping Structure for High-Speed Railway Under Different Seismic Excitations

There are many bridges and tunnels been built overlapping or close to each other during railway constructions in west or south China recent years. For bridge–tunnel overlapping structures on high-speed railway, serious damage or even complete destruction could be caused when powerful earthquake occurred in complex topography or poor geological areas. However, there is still little research yet on this kind of complex system taking interactions of bridge–tunnel–rock into account, especially for seismic damage or dynamic response mechanism. For purposes of dynamic response analysis and reasonable anti-seismic measures for complex bridge–tunnel overlapping structures, large scale shaking table model tests have been carried out. In shaking table model test, EL-Centro wave (EL) and the Wenchuan wave (WC) were adopted as loading wave in X, Y, Z-direction (perpendicular to the tunnel axis, horizontal along the tunnel axis, and vertical). Test results demonstrated significant differences existing on dynamic responses or variation laws especially in different seismic excitation cases, and fateful consequences could be caused. It also indicated that several sensitive and fragile parts (e.g., the arch vault and arch foot at enlarged section of the tunnel, at the end of the beam and the top of the abutment inside the tunnel portal, and the soil above the tunnel roof etc.) should be strengthened or required special treatment for structural security or overall stability. Simultaneously, seismic excitation combination analysis is important for such overlapping structures in weak surrounding rocks or soils. And the influence caused by the tunnel longitudinal direction should not be ignored for seismic response analysis for such structures. Bidirectional or multi-directional seismic excitation method is proposed for the rationality and accuracy on seismic tests or anti-seismic analysis for same or similar structures.