Effects of Soil–Foundation–Structure Interaction on the Seismic Response and Isolation Performance of a Large LNG Storage Tank at a Non-Bedrock Site

When large liquefied natural gas (LNG) storage tanks are constructed on deep non-rock sites, soil–foundation–structure interaction (SFSI) alters the dynamic characteristics of the system and affects the actual control effectiveness of the isolation layer. However, the current understanding of the coupling mechanism between the two remains insufficient. This paper takes a 220,000 m3 full-containment LNG storage tank as the study object and establishes a three-dimensional finite element model of the tank-pile group-site system in ABAQUS. Through comparative analyses of three model configurations, namely a rigid foundation model, a non-isolated model considering SFSI, and a lead-rubber bearing (LRB) isolated model considering SFSI, the SFSI effects and LRB isolation effectiveness are systematically separated. For the SFSI effects, the deep site attenuates medium- and high-frequency content while amplifying the response around approximately 1.6 Hz through site–foundation flexibility, transforming the heightwise acceleration amplification profile from an approximately linear pattern to a curvilinear one that bulges at mid-height, with peak pile-cap accelerations increasing by 25.1–76.9% relative to the rigid-base values. For the LRB isolation performance, the introduction of LRBs shifts the dominant system frequency below 1.0 Hz and reduces the maximum tank-wall acceleration amplification factor from 2.64 to 0.81. The resulting attenuation of superstructural inertial forces leads to reductions of 49.6–82.0% in pile-head shear and 57.4–78.0% in near-head bending moment, while the outer-to-inner pile-head moment ratio decreases from 2.94 to 1.13, indicating substantially improved pile-group force uniformity. Nevertheless, the beneficial effect of isolation diminishes with depth, and internal forces at abrupt soil-stiffness interfaces remain governed by kinematic interaction that the isolation layer cannot mitigate. The findings of this study can provide references for the seismic isolation design and pile foundation seismic optimization of super-large LNG storage tanks on deep overburden sites.