Abstract: With the development of underground space and uplift resistance issues arising during urbanization, the application of uplift pile technology in high water table clay areas, such as the southeast coastal regions, has become increasingly prevalent. However, conventional drilling techniques face significant challenges, including difficulty in achieving the required side resistance due to the mud cake effect and challenges in expanding the bottom hole. To address these challenges, a novel calculation method for the uplift bearing capacity of constrained grouting pile groups, accounting for disturbance effects, has been proposed. Taking the ⑤1 layer of grey clay in Shanghai as a case study, a clay and sand elastic-plastic-disturbed state concept(CASM-DSC) model was developed to accurately simulate the mechanical behavior of the soil around the pile. Numerical simulations were performed using a user-defined material constitutive (UMAT) subroutine to analyze the disturbance effects of the foundation soil around the pile and the influence of expansion size. The simplified calculation method for the uplift resistance of grouted and expanded steel pipe piles, as proposed in previous research, was revised. The results indicate that drilling excavation significantly reduces the side resistance of clay soils and influences the mechanical performance of the pile-soil interface. The disturbance coefficient and range exhibit a quadratic relationship with stress state and a linear reduction trend, respectively, in the foundation soil. At varying expansion lengths, the ultimate uplift bearing capacity of the model pile exhibits a “V” shape characteristic as length increases. Additionally, the expansion process alters the distribution of side force and axial force along the pile. Field tests at the Xuhui Binjiang site in Shanghai confirmed the effectiveness and applicability of the simplified calculation method, with a calculation error controlled within 15%. This provides reliable theoretical support and a practical calculation method for pile foundation engineering design.

Key words: constrained grouting pile, expanded size, disturbed state, uplift bearing capacity, simplified calculation method