Failure Mechanism and Ultimate Uplift Capacity Calculation Method for Belled Uplift Piles Considering Influences from Underground Water

As underground structures’ burial depth increases, buoyancy resistance due to groundwater becomes more pronounced. This study, through numerical simulation, analysis of field measurement data, and theoretical analysis, explores the impact of changes in groundwater level on the failure mode and uplift resistance of expanded base piles and proposes a new method for calculating the ultimate uplift capacity of expanded base piles considering the effect of groundwater. The research shows that the rise in groundwater level significantly affects the uplift performance of expanded base piles by altering the physical and mechanical properties of the soil and the morphology of the pile–soil failure surface, thereby affecting the pile's load-bearing capacity. The study identifies a three-segment failure mode for expanded base piles and notes that as the groundwater level rises, the extent of the failure surface gradually expands. Additionally, the paper underscores the importance of considering groundwater levels in practical engineering design and suggests re-evaluating the measured uplift capacity using the calculation method proposed in this study to ensure engineering safety. This research provides a theoretical basis and computational tools for designing belled uplift piles under the influence of groundwater, offering significant reference value for engineering practice.