Abstract:  To explore the dynamic response of overlapped tunnels under the action of seismic loads and provide a theoretical reference for the seismic design of overlapped tunnels, the distribution laws for peak acceleration values of upper and lower tunnels and crosssection of oblique overlapped tunnels are studied using a largescale vibration test platform under X unidirectional and XZ bidirectional ElCentro waves, respectively. The results show that: (1) The peak acceleration at the central crosssection of the overlapped tunnels is the highest, whereas those at the crosssections of the ends of the tunnels are significantly less; as such, the peak acceleration curve has a parabolic shape, indicating that the crown of the overlapped tunnel would be the weak point during earthquake resistance. (2) The seismic response of the invert at the crosssection of the upper tunnel is significantly weaker than that of the crown because of the undercrossing tunnel and spatial effect. Moreover, the dynamic response at the central crosssection of the invert of the undercrossing tunnel is the lowest, indicating that the failure mode of the invert shows a transmission evolution from both sides of the affected crosssection to the central crosssection. (3) Superposition effect is observed in the acceleration response of the central crosssection soil, leading to the strongest seismic response at this point. However, the acceleration amplification factors of other points decrease with increasing buried depth. (4) The dynamic response of a point under the  XZ  bidirectional seismic wave is much higher than that under the X unidirectional [HJ]seismic wave, especially when the seismic intensity is between 0.4 g and 0.6 g. Seismic waves with different loading directions diversely affect the seismic response at the invert of the overlapped tunnels.

Key words: overlapped tunnel, largescale vibration test platform, dynamic response, peak acceleration, acceleration amplification factor