Tunnels located in liquefiable soils are prone to flotation following earthquakes. When the shaking-induced pore water pressure buildup continues, saturated soil surrounding the tunnels liquefies, flotation occurs and the soil loses its shear resistance against the uplift force from the buoyancy of the tunnel. Mitigation of liquefaction-induced uplift of tunnels is one of the concerns of geotechnical engineers. This article aims to investigate the efficacy of the available mitigation techniques using a finite element program with an emphasis on the prediction of excess pore water pressures in the surrounding soil and the uplift of the tunnel. In addition to the conventional techniques, a newly developed technique Partial Saturation was modeled to examine its effect on the reduction of the tunnel uplift. A parametric study was done to compare the effectiveness of partial saturation with other mitigation techniques. Results showed that the partial saturation technique would effectively dissipate the excess pore water pressure in the soil around the tunnels. It also performs well in the reduction of the uplift of the tunnel. The most appealing advantage of this technique against the other available mitigation techniques is that it can be employed easily without disturbing the soil around the tunnels. A new methodology to numerically simulate the partially saturated sands was described in this paper.

Tunnels buried in liquefiable soils are prone to liquefaction-induced uplift damage during strong earthquakes. Studying the parameters that affect the liquefaction-induced uplift of tunnels is crucial for enhancing the seismic resilience of tunnels, minimizing potential damage, and ensuring the safety of critical infrastructure during strong earthquakes. This study investigates the effects of tunnel diameter (D), burial depth (H), and amplitude of input shaking at the base of the soil layer (amax) on the liquefaction-induced uplift of circular tunnels using numerical simulation. A comprehensive parametric study was conducted to investigate the effect of the H/D ratio and the value of amax on the dynamic responses, such as uplifts and internal forces in the lining of the tunnel. Using the numerical results, an empirical function was proposed to estimate the liquefaction-induced uplift of circular tunnels buried in liquefiable, loose soils. Finally, the results predicted by the proposed function were compared with those of a shaking table test and a centrifuge experiment. It has been demonstrated that the burial depth of a tunnel has the greatest impact on its seismic performance. Under identical input motion, increasing the burial depth of a tunnel with a 5-m diameter from 5 to 10 m resulted in a 270% increase in uplift and increased the internal forces in the tunnel lining, noticeably.