Abstract: In order to provide reference for the seismic design of the portal in the bridge-tunnel connected system, the failure process of the portal was studied through the large-scale shaking table tests, and obtained the acceleration signals which were quantitatively analyzed by wavelet packet transform. It is found that the failure of the portal is marked with the appearance of the crack in the vault slope. The unsafety degree of tunnel portal in the bridge-tunnel connected system ranks as the vault, the abutment, the slope and the invert in turns under the action of ground motion. The strength and stiffness of the bridge and tunnel are relatively high and therefore, the failure often starts from the slope, then the vault and abutment, while the damage of the invert is generally slight. The seismic wave with a low-frequency (0.1?12.51 Hz) plays a leading role in the failure process of the portal-slope system. Due to the complex refraction and reflection effect between the different material interfaces, the low-frequency waves will change drastically before propagating from soil into concrete structures. By analyzing the changes in the percentage of the energy of the low-frequency waves, the failure of portal-slope system can be divided into three stages, i.e., the elastic deformation stage under the small-shake, the small elastic-plastic deformation stage under the medium-shake, and the large failure deformation stage under strong-shake.

Key words: bridge-tunnel connected system, large-scale shaking table test, portal section, dynamic response, wavelet packet transform