Experimental investigation of the seismic response and ultimate lateral resistance of pile–superstructure systems considering ground settlement due to pore water dissipation

This study investigates the seismic response and ultimate lateral resistance of pile–superstructure systems subjected to repeated earthquake loadings in liquefiable ground. A series of centrifuge model tests was conducted using scaled specimens (1/40 scale) to reproduce the progressive process of ground settlement, pile head exposure, and pile failure under multiple shakings. The tests successfully simulated liquefaction-induced ground settlement and consolidation, leading to pile damage dominated by local buckling near the pile head. Spectral analyses of acceleration records before liquefaction revealed that, while settlement and soil densification had only a limited influence on the system's natural period, pile plasticization played a dominant role in lengthening the period. Comparison between inertial forces of the superstructure and measured pile head shear forces demonstrated good agreement, validating the data correction methods and skeleton curve adopted. It was observed that, when liquefaction occurred, superstructure responses decreased markedly, and pile axial forces fluctuated less. Plastic hinge development was traced through bending moment histories, and final failure was attributed to local buckling, consistent with visual inspection of the specimens. The ultimate lateral resistance of the pile foundation, accounting for ground settlement, was found to decrease by approximately 8.3 % compared to the initial state. These findings highlight the significance of time-dependent ground changes, such as consolidation-induced settlement and liquefaction, in long-life structures. The results contribute to establishing design methodologies for pile foundations that explicitly incorporate inevitable ground property changes during service life. • Centrifuge tests reproduced progressive pile failure under repeated seismic shaking. • Ground settlement and pile head exposure effects on seismic response were clarified. • Liquefaction and consolidation were modeled in one physical test sequence. • Period elongation linked mainly to pile material nonlinearity, not ground densification. • Ultimate lateral resistance decreased by 8.3 % with ground settlement considered.