Fiber reinforcement has been demonstrated to mitigate soil liquefaction, making it a promising approach for enhancing the seismic resilience of tunnels in liquefiable strata. This study investigates the seismic response of a tunnel embedded in a liquefiable foundation locally improved with carbon fibers (CFs). Consolidated undrained (CU), consolidated drained (CD), and undrained cyclic triaxial (UCT) tests were conducted to determine the optimal CFs parameters, identifying a fiber length of 10 mm and a volume content of 1 % as the most effective. A series of shake table tests were performed to evaluate the effects of CFs reinforcement on excess pore water pressure (EPWP), acceleration, displacement, and deformation characteristics of both the tunnel and surrounding soil. The results indicate that CFs reinforcement significantly alters soil-tunnel interaction dynamics. It effectively mitigates liquefaction by enhancing soil stability and slowing EPWP accumulation. Ground heave is reduced by 10 %, while tunnel uplift deformation decreases by 61 %, demonstrating the stabilizing effect of CFs on soil deformation. The fibers network interconnects soil particles, improving overall structural integrity. However, the increased shear strength and stiffness due to CFs reinforcement amplify acceleration responses and intensify soil-structure interaction, leading to more pronounced tunnel deformation compared to the unimproved case. Nevertheless, the maximum tunnel deformation remains within 3 mm (0.5 % of the tunnel diameter), posing no significant structural risk from the perspective of the experimental model. These findings provide valuable insights into the application of fibers reinforcement for improving tunnel stability in liquefiable foundations.

To research the effect of vertical earthquakes on rectangular underground structures in inclined liquefied foundations, and explore the seismic response characteristics of the structure with bidirectional earthquake, the finite element-finite difference coupled numerical method is used. The results revealed that the vertical earthquake will increase the degree of soil liquefaction in the vicinity of the structure and the dynamic response of the structure. The influence is related to the type and amplitude of the seismic wave. The displacement of the subway station will increase gradually as the compactness of the sand decreases or the angle of inclination of the ground increases. The lateral displacement of the subway station mainly occurs during the earthquake, and the vertical displacement mainly occurs after the earthquake. In addition, in the inclined site, the vertical displacement and internal force of the left and right sides of the underground structure and the excess pore water pressure ratio of the soil are not symmetrically distributed along the central column, and the closer to the bottom at the slope, the larger the settlements of the structure produce to make the whole structure rotate. The study can provide some seismic strengthening suggestions for underground structures in the inclined liquefiable site with bidirectional earthquakes. The seismic design of underground structures also needs to take into account the effects of the structure rotation during an earthquake in the inclined liquefiable site.