To investigate the dynamic response and failure characteristics of the portal section of a loess tunnel under seismic action under different rainfall intensities, two working conditions – heavy rain (80 mm/24 h) and extreme rainstorm (170 mm/24 h) – were set up for shaking table model tests. Acceleration sensors and strain gauges were used to collect dynamic response data of the tunnel and slope, revealing the deformation patterns and failure mechanisms of the tunnel lining and soil under the coupled effect of rainfall and earthquake. The results show that rainfall intensity significantly affects the dynamic response of the tunnel structure. Under extreme rainstorm conditions, axial cracks appear earlier in the tunnel, and the soil is more prone to liquefaction. The vault and invert are the most sensitive areas for acceleration response, especially under Z-direction loading, showing significant nonlinear amplification effects. The left springing is the strain concentration zone, exhibiting obvious asymmetric pressure characteristics. As seismic intensity increases, the strain response of the lining transitions from linear to nonlinear, with 1.0 g being the threshold for structural degradation. Rainfall exacerbates seismic damage in the portal section of loess tunnels, and under extreme rainstorm conditions, the structure is more likely to enter the plastic stage and fail. It is recommended to strengthen key parts such as the vault, invert, and springing in the seismic design of loess tunnels, and to consider the impact of coupled horizontal and vertical ground motions.
Wang et al. (Sun,) studied this question.