Seismic performance and fragility for a shallow-buried subway station under horizontal and three-dimensional isolation

Column-top isolation can reduce the seismic demand of shallow-buried subway stations, yet the relative performance of horizontal and three-dimensional isolation under different ground-motion types remains insufficiently understood. A two-story, three-bay subway station in Xi’an was investigated using three configurations: the original station (OS), the retrofitted station with horizontal isolation (RS-HI), and the retrofitted station with three-dimensional isolation (RS-3DI). RS-HI employs a nonlinear friction-sliding unit, while RS-3DI incorporates an additional vertical disc-spring assembly. A finite element (FE) model accounting for soil-structure interaction was validated against a 1/40-scale shaking-table test. Incremental dynamic analyses (IDA) were then conducted using 25 near-fault pulse-like (NFP), near-fault non-pulse-like (NNP), and far-field (FF) ground motions. Both isolation schemes reduce damage at the central-column ends through response redistribution, while the side-wall response remains within the deformation-capacity envelopes. The relative effectiveness of the two schemes depends on ground motion type and intensity. The two schemes perform comparably under FF motions and NNP motions of low and moderate intensity. RS-3DI provides greater damage control as NNP intensity increases and exhibits its clearest advantage under NFP motions. At a peak ground acceleration (PGA) of 0.60 g under NFP excitation, RS-3DI reduces the probability of severe damage from 12.97 % for OS to 1.42 %. These findings provide a basis for selecting appropriate isolation schemes for shallow-buried subway stations under different seismic environments.