Systematic seismic simulation for nuclear island buildings in CPCRF site: Insights into interfacial discontinuity

Abstract

Nuclear facility sites built on soft deposits often adopt a combined piled cushion raft foundation (CPCRF) to enhance bearing capacity. However, separation and slip at the raft–bottom interface is inevitable in refined seismic simulations of weakly anchored nuclear island buildings (NIBs). Multiple factors related to both the structure and foundation influence the interface behavior. To address this, a structure–interface–soil nonlinear interaction model was developed, incorporating interfacial discontinuity characteristics, tri-directional wave inputs, and a stable semi-unbounded condition. The validity of the wave–field simulation method and the interface model were confirmed through theoretical comparisons. Using the AP1000 NIB at a specific CPCRF site as an example, the practicability of the model was validated, and key behavioral patterns were identified. In the static-seismic process, correlations between interface behavior, pile damage, and structural vibration were quantitatively elucidated. When seismic intensity exceeded design limits, the minimum instantaneous grounding ratio decreased rapidly. Structural vertical acceleration nearly doubled, and the frequency band of peak horizontal vibration shifted to higher frequencies. Interface behavior strongly correlated with slip stability and pile body damage. These findings indicate that interfacial discontinuities at the raft's bottom pose safety risks warranting further investigation.