三向地震作用下叠交隧道地震响应振动台试验研究

Shaking table test on seismic response of stacked tunnels under three-directional earthquake wave excitation

叠交隧道是涉及隧道之间、隧道与土体相互作用的复杂体系,其安全性将严重影响城市轨道交通建设。目前,对于叠交隧道振动台试验的研究集中在水平平行和交叉叠交隧道、单向和双向地震动输入。鉴于此,利用自行设计的层状三向剪切模型箱,对竖直平行叠交隧道开展三向地震作用下的振动台模型试验,研究地基土-叠交隧道模型体系动力特性、地基土加速度、叠交隧道加速度、地表沉降、地基土孔压、叠交隧道动土压力及叠交隧道应变等地震响应。结果表明:随着震波峰值加速度(peak ground acceleration,简称PGA)依次增加,地基土-叠交隧道模型体系的自振频率随之减小,而阻尼比随之增大;叠交隧道周围地基土加速度和孔压的梯度差随着地震波PGA的增大而增大,且上隧道周围梯度差比下隧道更大;地基土对加速度的放大效应随着地震波PGA的增大而减弱;相同地震波作用下,相同位置处的叠交隧道加速度傅里叶谱形状相似,但幅值随着地震波PGA的增大而增大。此外,与顶部和底部位置相比,腰部位置加速度傅里叶谱频段范围变宽,幅值峰值有所降低;地表沉降峰值随着地震波PGA的增大而减小,相比地基土两侧位置,中心位置的沉降峰值明显较小;地震波的类型对叠交隧道动土压力峰值和应变峰值影响较小;对于动土压力峰值,两隧道的最大值均为腰部,而上、下隧道的最小值分别为底部、顶部;对于应变峰值,上隧道在腰部明显大于顶部和底部,而下隧道在4个位置相差不大。

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.