Influence of diaphragm wall on seismic responses of large unequal-span subway station in liquefiable soils

Ground liquefaction is one of the severest threats that ensue subsequent damage to the subway underground structure during and after strong earthquakes. However, few studies on the seismic response of large-scale subway underground structures in liquefiable site, especially for complex subway stations, have been reported. Existing researches that consider the diaphragm wall as safety reserve for the seismic design of subway stations are oblivious of the influence of the diaphragm wall on the deformation and uplift of underground structures. Contradictory to the original intention, the diaphragm wall may have adverse effects on the overall deformation behavior and force redistribution of the structure. Thus comprehensive exploration of the interaction between the diaphragm wall and the subway station in liquefiable site during and after earthquake should be carried out to rationalize the design of the underground structure. Numerical simulations of the seismic response of different soil-structure interaction systems are implemented and discussed in the present study. In the numerical simulation, the constitutive model for saturated sand and the Arbitrary Lagrange-Euler (ALE) method to prevent mesh distortion are applied to constitute the static and dynamic coupling finite-element model. Earthquake responses of the soil and the complicated underground subway station are then investigated. Modeling results are analyzed in respect of earthquake responses yielding the liquefaction distribution of the site, the uplift feature of the unequal-span subway station, the dynamic settlement and vector characteristics of the surrounding soil, the lateral deformation and the earthquake-induced damage of the underground structure. It is found that the uplift of the unequal-span subway station is featured by uneven uplift across the spans. When the diaphragm wall is installed, the tension damage degree of the bottom plate of the subway station are intensified, while the components of cantilever span in the upper layer suffer the less. The resulted new findings from this study shed light on the seismic performance and seismic design method for the unequal-span subway stations at a liquefaction site.