Influence of Soil–Structure Interface Modeling on Seismic Response of Buried Nuclear Facilities in Non-Bedrock Sites

In this study, the seismic response of the buried structure of a nuclear power plant (NPP) located on a non-bedrock site is investigated using a three-dimensional finite element model incorporating soil–structure interaction (SSI). Three distinct soil–structure connection methods are compared: node-to-node bonded connection (NNBC), multi-point constraints (MPCs), and separable contact elements (SCEs). The results indicate that the NNBC and MPC models show a restraining effect of the structure on the seismic response of the surrounding soil, whereas the SCE model amplifies the soil response adjacent to the structure and yields significantly greater structural responses. Quantitatively, relative to the NNBC model, the SCE model increases the mean ground-surface and mean in-structure peak spectral accelerations by about 23% and 93%, with a peak soil–structure relative displacement of 0.81–0.98 cm. This study concludes that the choice of soil–structure connection method significantly influences the finite element simulation results for non-bedrock sites. Further research is needed to determine the appropriate connection methods for different soil layers.