Abstract: Stacked tunnels is a complex system involving the interaction between tunnels and between tunnel and soil, and its safety will seriously affect the construction of urban rail transit. At present, the research on shaking table test of stacked tunnels focuses on horizontal parallel and cross arrangements, unidirectional and bidirectional ground motion input. This paper uses a self-designed three-dimensional laminar shear soil container to implement a shaking table model test on seismic response of vertical parallel stacked tunnels under three-directional earthquake wave excitation. Its seismic response includes the dynamic characteristics of foundation soil-stacked tunnels model system, the acceleration of foundation soil and stacked tunnels, ground settlement, the pore pressure of foundation soil, and the dynamic soil pressure and the strain of stacked tunnels. The results show that with the increase of seismic wave peak ground acceleration (PGA), the natural frequency of foundation soil-stacked tunnels model system decreases and the damping ratio increases. The gradient difference of soil acceleration and pore pressure around the stacked tunnels increases with the increase of seismic wave PGA, and the gradient difference around the upper tunnel is larger than that around the lower tunnel. The amplification effect of the foundation soil on the acceleration decreases with the increase of the seismic wave PGA. Under the action of same seismic wave, the shape of the acceleration Fourier spectrum of stacked tunnels at the same position is similar, but the amplitude increases with the increase of the seismic wave PGA. Furthermore, compared with the crown and bottom positions, the frequency range of the acceleration Fourier spectrum at the waist position becomes wider, and the peak amplitude decreases. The peak value of ground settlement decreases with the increase of seismic wave PGA, and the peak value of ground settlement in the center is obviously smaller than that on both sides of the foundation soil. The type of seismic wave has little effect on the peak value of dynamic earth pressure and strain of stacked tunnels. For the peak dynamic earth pressure, in the upper tunnel, the maximum value of the two tunnels is at the waist position, while the minimum value of upper and lower tunnels is at the bottom and crown positions, respectively. The peak strains at the both waist positions in the upper tunnel are significantly larger than those at the top and bottom positions, while the peak strain does not differ much at the four positions in lower tunnel.

Key words: shaking table test, stacked tunnels, seismic response, three-directional earthquake wave excitation