Shaking table test and numerical simulation on ultra-large diameter shield tunnel passing through soft-hard stratum

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. •Shaking table test on ultra-large diameter tunnel passing through soft-hard stratum.•A modified similitude-ratio design method is proposed, with the soil-structure relative stiffness as the main control factor.•The comparison between test and numerical results shows a good agreement.•The tunnel seismic response around the soft-hard interface is investigated.