Shaking table tests on the liquefaction-induced uplift displacement of circular tunnel structure

Underground structures are susceptible to float and move upward during earthquakes when located in a liquefiable soil deposit. There are examples of this phenomenon in past major earthquake events. In this study, the uplift of circular tunnels in a liquefiable sand layer was investigated with a series of shaking table tests. The research has focused on the buried depth of the tunnel, tunnel diameter, tunnel weight, liquefaction extent, uplift mechanism, and factor of safety against liquefaction-induced uplift. According to the test results, the shallow buried depth, larger diameter, and lower weight can intensify the tunnel uplift, so the displacement in post-liquefaction time continues at the same rate as during the shaking time. Due to the shear-induced dilation, pore water pressure generation around the tunnel was reduced compared with that of the free field. The excess pore water pressure dissipation in the soil overlying the uplifted tunnel was significant, which leads to suction in the soil deposit. Furthermore, the acceleration response of overlying soil with the uplifted tunnel was similar to that of the free field. However, the soil acceleration response around the tunnel without uplift was similar to the base motion.