Influence of Near-Fault Unidirectional and Bidirectional Ground Motions on DSM-Enhanced Reactor Building Foundations Considering Soil–Structure Interaction: A Case Study

This study examines the seismic performance of the APR۱۴۰۰ nuclear reactor, focusing on soil–structure interaction (SSI) and structure–soil–structure interaction (SSSI), particularly on foundations enhanced with block deep soil mixing (DSM). The reactor, including its internal structure, containment building, and DSM layers, was modeled to evaluate its dynamic response to unidirectional and bidirectional near-fault ground motions with different frequency contents. Results indicate that the internal structure experiences higher horizontal accelerations than the containment building, while rocking-induced vertical accelerations are significant in the containment. DSM effectiveness depends on the frequency content of the ground motion, soil properties, and DSM depth. Horizontal accelerations are largely unaffected at high frequencies, but low-frequency responses are notably reduced. In the vertical component, accelerations in the ۲–۱۰ Hz range increase by over ۱۴۰% in the containment building and nearly ۶۰% in the internal structure for an ۱۸-m DSM layer, highlighting the vulnerability of many reactor components. Morlet wavelet analysis shows that DSM reduces horizontal-acceleration energy transmitted to the containment building while shifting it to higher frequencies. In contrast, vertical-acceleration energy is substantially amplified, particularly in the ۳–۷ Hz range. SSSI effects significantly influence structural response: for modeling a second reactor at a ۳۰-m distance, horizontal energy decreases by approximately ۳۴% in the internal structure, while vertical acceleration energy increases by ۳.۲ times; at ۷۰-m spacing, vertical energy rises by up to ۸ times. Bidirectional near-fault excitations further increase vertical accelerations by ۶–۴۶ times compared to unidirectional loading, depending on the structure and earthquake. These findings underscore the critical importance of accounting for multidirectional excitations, DSM-induced effects, and SSSI in the seismic design of nuclear facilities, particularly for sensitive equipment and high-frequency structural responses. Accurate evaluation of these factors is essential to ensure operational safety and prevent potential damage to reactor components under severe near-fault ground motions.

کلیدواژه ها:

Finite-element modelling ، Deep soil mixing ، Multidirectional loading ، Rocking motion ، Nuclear power plant