In this study, the seismic behavior of a shield tunnel with an ultra-large diameter of 15 m passing through a soft-hard stratum was investigated, using a series of 1/30 scaled shaking table model tests and numerical simulations. A modified similitude-ratio design method was proposed, with the soil–structure relative stiffness as the main control factor. The model tunnel was made of a plexiglass tube. The soft soil was modeled with silty clay, whereas the hard soil was modeled with fine and angular gravel. The tests were also simulated using the finite element modeling (FEM) software ABAQUS, and equivalent linearization was employed for the soil nonlinearity in the frequency domain. The results show that the modified similitude-ratio design method is workable and effective. Moreover, it may provide additional possibilities regarding the selection of structural model materials, and broaden the applicability of a shaking table with a conventional loading performance. The strain of the tunnel around the soft-hard interface increases significantly, and the maximum strain occurs within the range of 1 D (D is the outer diameter of the tunnel) in the soft soil near the interface along the direction of tunnel's length. In one observation section, the largest strain appears at the crown or bottom, followed by those at the spandrel, haunch, and knee. The region affected by the soft-hard interface is approximately 1 D in the hard soil and 2 D in the soft soil. The accelerations in the hard and soft soil are amplified, and the acceleration amplification factors gradually decrease with an increase in the excitation amplitude. The peak ground acceleration in the soft soil is smaller than that in the hard soil in the case with a larger excitation amplitude. The tunnel is curved in the vertical direction, owing to the soft-hard stratum. This study may provide a reference for shaking table tests for ultra-large diameter shield tunnels at complex sites.

在这项研究中，使用一系列的1/30比例振动台模型试验和数值模拟，研究了穿过软硬地层的超大直径15 m盾构隧道的地震行为。提出了一种以土-结构相对刚度为主要控制因子的拟似比设计方法。模型隧道由有机玻璃管制成。用粉质粘土对软土进行建模，而用细而有角度的砾石对硬土进行建模。还使用有限元建模（FEM）软件ABAQUS对测试进行了仿真，并在频域中对土壤非线性采用了等效线性化。结果表明，改进的相似比设计方法是可行和有效的。而且，它可以提供有关结构模型材料选择的其他可能性，并可以扩大具有常规加载性能的振动台的适用性。在软硬界面周围的隧道应变显着增加，并且最大应变发生在沿隧道长度方向的界面附近的软土中的1 D范围内（D是隧道的外径）。在一个观察区域中，最大的应变出现在冠或底部，其次是在跨度，臀部和膝盖。受软硬界面影响的区域在硬土中约为1 D，在软土中约为2D。硬土和软土中的加速度被放大，并且随着激励振幅的增加，加速度放大因子逐渐减小。在激发幅度较大的情况下，软土的峰值加速度小于硬土的峰值加速度。由于软硬地层，隧道在垂直方向上是弯曲的。该研究可为复杂地区超大直径盾构隧道的振动台试验提供参考。