Abstract: In deep soft-soil regions, rigid-pile composite foundations have increasingly exhibited basal voids and abnormal inter-pile soil settlement during post-construction service. Using the Chaoshan Ring Expressway project as a case study, this paper investigates the deformation mechanism of pile-soil interaction driven by non-loading factors. A coupled hydro-mechanical numerical model was developed based on site-specific geotechnical parameters to systematically evaluate the respective contributions of groundwater-level fluctuations, under-consolidation of soft soil, and pile-installation disturbance to inter-pile soil settlement. The results indicate that three non-loading mechanisms dominate the observed settlement: (i) increased effective stress induced by abrupt groundwater drawdown, (ii) self-weight consolidation of under-consolidated soft soil, which may reach up to 12 cm, and (iii) long-term dissipation of excess pore pressure generated by soil displacement during pile installation. The consolidation-driven deformation triggered by these factors is identified as the primary cause of basal voids beneath rigid-pile composite embankments. The findings highlight the need to account for long-term hydrological variations and construction-induced disturbances in both design and maintenance. Overall, soil consolidation and deformation induced by non-loading factors constitute the governing mechanism behind void formation in rigid-pile composite foundation embankments.

Key words: Rigid Piles, Void at Base Slab, Groundwater Level Fluctuation, Underconsolidation, Piling Disturbance