Cloud and incremental dynamic analysis (IDA) are the two most commonly used methods for seismic fragility analysis. The two methods differ significantly in the number of ground motions and whether these motions are scaled. This paper designed a random selection procedure to thoroughly discuss the influence of ground motion combinations encompassing different numbers of motions on the Cloud-based and IDA-based seismic fragility analysis for underground subway station structures. Focusing on a shallow-buried single-story station structure, a nonlinear dynamic time-history finite element analysis model of soil-structure interaction was developed. 400 ground motions were selected for random combination to perform Cloud-based seismic fragility analysis, and 20 ground motions were selected for random combination to perform IDA-based analysis. The results showed that the number of ground motions has a significant influence on the seismic fragility analysis in both Cloud and IDA, especially on the prediction of damage probability for higher seismic performance levels and when the PGA exceeded 0.3 g. In regions with a low probability of strong earthquakes, this paper recommended using no fewer than 10 and 220 ground motions in the IDA-based and Cloud-based seismic fragility analyses, respectively. In regions with a high probability of strong earthquakes, the optimal number of ground motions should be increased to 300 for Cloud-based analysis and 15 for IDA-based analysis.

This study focuses on the Yanmazhuang West Station and Jinan West Railway Station of Jinan Rail Transit Line 1, China, examining the dynamic characteristics of eight-layered silty clay and subway station responses in Jinan. Through shaking table model tests, including free-field, two-story two-span, and three-story three-span stations, it finds relationships between the silty clay's dynamic shear modulus ratio and strain, damping ratio and strain, and confining pressure and dynamic shear modulus. It also reveals soil and station structural seismic responses to different intensities and waves.

Due to the planning of the subway route, it is difficult to avoid crossing soft soil site conditions at subway stations. The seismic response of subway station structures is closely related to the surrounding soil site. In this paper, centrifuge shaking table tests were designed and carried out for subway station structures at three typical soft soil sites (all-clay site, liquefiable interlayer site, and fully liquefiable site). The test results are as follows. The structure is most severely damaged in all-clay site, while the damage is low in liquefiable interlayer site and fully liquefiable site. For liquefiable sites, site liquefaction results in a lower soil-structure stiffness ratio. Thus liquefiable interlayer site and fully liquefiable site provide a natural seismic isolation system for structures compared to all-clay site. The limits of the inter-story drift ratio of the structure were used to evaluate the post-earthquake performance stages of the model structure in the three sites. In all-clay site, the structure is in the immediately operational stage after the loading condition of 0.1g and 0.32g, and in the reparable operational stage after the loading condition of 0.52g and 0.72g. In the liquefiable interlayer site and full liquefiable site, the underground structure is in the normal operational stage after the loading condition of 0.1g and in the immediately operational stage after the loading condition of 0.32g-0.72g.

The experimental approach is crucial for investigating the seismic performance and damage process of underground structures. Considering the shortcomings of the 1-g, centrifuge shaking table and monotonic displacement pushover tests, a large-scale cyclic displacement pushover test method is proposed based on the soilunderground structure dynamic interaction and seismic performance quantification system. Taking a twostory three-span subway station structure as the prototype, the cyclic displacement pushover test device was designed for a 1/7-scale multi-story subway station based on the seismic response characteristics of underground structures. The corresponding numerical simulations and experiments were conducted. Typical numerical results (including the seismic damage process, capacity curves of the structural columns, and strain response) and test results (the macroscopic phenomenon of structural damage development, strain response, and deformation response) are interpreted. The results show that the proposed cyclic displacement pushover test is better than the monotonic displacement pushover test, the damage process of the tested station structure conforms to the description of the inter-story drift ratio (IDR) quantification system of seismic performance. Meanwhile, the column has greater strain amplitudes than other components, and the column strain curves reach their peaks before other components. Furthermore, the tested station structure has a similar damage pattern to the Daikai subway station. The reliability and feasibility of the proposed cyclic displacement pushover test method are verified.

Challenges related to seismic performance and seismic mitigation are more pronounced in the presence of weak interlayers compared to typical layered soil conditions. This study focuses on a double-layer double-span rectangular frame subway station structure. A coupled static-dynamic finite element analysis model of the soil-structure system is established by using the finite element software ABAQUS/CAE V 6.14. The research investigates the influence of factors such as interlayer thickness, location, and strength on the seismic response of subway station structures. Furthermore, in order to evaluate the effectiveness of FPB in mitigating seismic effects in the weak interlayer ground, two different schemes are proposed in this paper. One is the structure without FPB and the other is the structure with FPB on the top of the central column. The findings reveal that weak interlayers exert a significant influence on the seismic response of subway station structures, especially when these lower-strength weak interlayers are located within the central portion of the subway station structure and exhibit considerable thickness. The FPB on the top of the central column can reduce the overall lateral stiffness of the subway station structure. This, in turn, results in a slight increase in the deformation of sidewall and inter-story displacement angles, accompanied by a marginal exacerbation of sidewall damage. However, the implementation of FPB effectively reduces the deformation of the central column and substantially mitigates the extent of damage to the central column.

Research on the characterization of ground motion intensity and damage of underground structures is limited, while reasonable selection of ground motion intensity measures and structural damage measures is a crucial prerequisite for structural seismic performance evaluation. In this study, a two-dimensional finite element model of soil and structures was established based on the Daikai subway station in Japan. Through incremental dynamic analysis, 32 ground motion intensity measures and seven structural damage measures were comprehensively evaluated from seven properties, including efficiency, practicality, proficiency, scaling robustness, relativity, hazard computability, and sufficiency. According to the analysis results, the purpose and significance of each property during measure optimization were hierarchically sorted out. The results show that peak ground acceleration, acceleration spectrum intensity, and sustained maximum acceleration are recommended as ground motion intensity measures, while maximum inter-story drift ratio, column end displacement angle, and two-parameter measures are recommended as the structural damage measures for seismic performance evaluation of the shallow-buried subway station. Furthermore, measure optimization approaches are proposed as follows: the basic selection of IMs should satisfy scaling robustness, hazard computability, and sufficiency to site condition; the optimal selection of IMs is suggested to be evaluated mainly through efficiency, practicality and proficiency, and verified through relativity and relative sufficiency between IMs. The optimal selection of DM is suggested to be evaluated through four properties, including efficiency, practicality, proficiency, and relativity.

In recent years, the prefabricated subway station structure (PSSS) has become a hot spot of underground structure research. In this paper, the numerical model of a soil-subway station structure in a slowly inclined liquefiable site at the surface is established by using FLAC3D finite difference software. And the applicability of the PSSS under the gently inclined liquefiable site is investigated through the foundation pore water pressure, lateral movement of liquefied soil, and dynamic response and uplift characteristics of the subway station structure. It is found that under the gently inclined liquefiable site conditions, the PSSS exhibits tilting and floating behaviors and has an anti-liquefaction effect within a certain range of surrounding soil layers. Compared with the same type of cast-in-place subway station structure (CIPSSS), it has better resistance to overturning and uplift, and the structure has less stress. Under the premise of ensuring static waterproofing, the PSSS can be applied to surface inclined liquefiable sites.