Abstract: The determination of the axial bearing capacity of large-diameter steel pipe piles is a crucial aspect of the design of pile foundations. However, the existing methods for calculating the axial bearing capacity of pile foundations are mostly based on the test results of closed-ended piles or small-diameter steel pipe piles, and these methods are not applicable to large-diameter steel pipe piles. Based on the existing pile foundation bearing capacity calculation methods based on cone penetration tests, a modified method is proposed. By comprehensively considering the Poisson's effect, soil plugging effect, and side resistance degradation, an expression for the pile side friction resistance is derived. Meanwhile, the base resistance is divided into two parts: annular resistance and inner shaft resistance, and the proportional relationship between cone-tip resistance and these two resistances is established. The modified method is used to calculate the axial bearing capacity of large-diameter steel pipe piles in an actual offshore engineering project, and the results are compared with those obtained using six commonly used existing methods. The results show that compared with the existing methods, the modified method is more accurate, especially in terms of the prediction accuracy of pile side friction resistance. Additionally, sensitivity analyses of key parameters, including pile diameter, pile length, plug length ratio, and cone tip resistance, demonstrate that the soil plug effect significantly influences the calculation of the vertical bearing capacity of large-diameter steel pipe piles in both non-cohesive and cohesive soils. The research results can provide theoretical guidance for the calculation of the axial bearing capacity of large-diameter steel pipe piles.

Key words: large-diameter steel pipe piles, cone penetration test (CPT), axial bearing capacity design methods, soil plugging effect