High-performance seismic response analysis for mega-scale integrated underground-aboveground structure system in saturated sand.

With rapid urbanization, major cities are witnessing mass development of large integrated underground-aboveground structure systems. A notable example is the Beijing Municipal Administrative Center Transport Complex (BMACTC), which boasts an underground area spanning 1.28 million square meters. The soil-structure interaction and mutual interaction among structure components, particularly in liquefiable sites, pose significant challenges for seismic design. To address these challenges, this study proposes a high-performance solid-fluid coupled elastoplastic simulation method for earthquake geotechnical engineering, and applies it to achieve integrated simulation of BMACTC with a finite element method (FEM) model of over 16 million degrees of freedom. The analysis unveils the seismic response of underground structures under the influence of large openings, aboveground structures, and cross-section changes. Saturated sand layers experience significant weakening under seismic loading, with a maximum excess pore pressure ratio of nearly 0.5. The large openings significantly increase the nearby horizontal deformation and uplift of the underground structure. Moderate height and tall aboveground structures have different effects on the deformation of the underground structure, which is related to the system natural frequency and input motion frequency. The change in cross section geometry affects the deformation and internal force in the transition zone between the different sections.