Effect of flexibility ratio on seismic response of rectangular tunnels in sand: Experimental and numerical investigation

The flexibility ratio(F) is defined as the stiffness of a structure relative to that of soil, a critical factor affecting the soil-structure interaction. This study aimed to investigate the effect of F on the seismic response of rectangular tunnels constructed in sand. Shaking table tests were performed based on a scale model of a tunnel with different stiffness values. A 3D finite element model was established using ABAQUS, and the numerical results were compared with the test results. Subsequently, the verified model was implemented in a parametric study. The results showed that tunnels with lower F have higher acceleration responses in the high frequency-range of input motions. In addition, the amplification of the ground acceleration decreases with an increase in F, and the maximum response occurs in a longer period relative to the free-field. The distribution of the dynamic earth pressure along the tunnel lining with different F is relatively complex; nevertheless, overall, rigid tunnels have greater values than flexible tunnels. The dynamic bending moment along the tunnel sidewall decreases with increasing F, but it has the same trend along the sidewall. The presented results may lead to a better understanding of the seismic response of rectangular tunnels constructed in sand, providing practical references for the seismic design of similar underground structures.