Seismic response of shield tunnel structure embedded in soil deposit with liquefiable interlayer

Shield tunnels are widely in used urban areas and could be constructed in fully or partially liquefiable soil deposits and are thus susceptible to damage during earthquake events. In this paper, a two-dimensional saturated soil-structure dynamic interaction model is developed for shield tunnel lining structures. The model accounts for the nonlinear mechanical behaviors of the shield tunnel segments and joints. It also accounts for the soil nonlinear behavior by employing plasticity models (i.e., PM4Sand and PM4silt for sand and plastic silt/clay, respectively). The seismic response of the shield tunnel structure in soil deposit with liquefiable interlayer as well as the interaction mechanism between the liquefiable soil layer and the tunnel are investigated. The obtained results demonstrate that the sand dilatancy and cyclic mobility behaviors under undrained loading conditions govern the seismic site response and that the presence of tunnel structure changes the site acceleration response and degree of soil liquefaction. It is also found that internal forces and deformations of the tunnel segment joint around the foot and shoulder are significantly larger than that in the rest of joint positions. Therefore, particular attention should be paid to potential damage of joint bolts around the foot and shoulder in a liquefiable soil deposit.