Evaluation of the Lateral Load Response of Large-Diameter Flexible Single-Pile Foundations in Sand: A Novel <i>p</i> – <i>y</i> Curve Approach

Current design practices for single piles in sandy soil often model the pile as a series of beam elements connected to p–y curves to represent soil–pile interaction. However, standard p–y curves for sandy soil are primarily based on field test results for slender, flexible piles with a length-to-diameter ratio greater than 20, neglecting critical factors such as pile configuration, pile–soil rigidity, and soil parameters. Increasing evidence highlights the limitations of this approach, underscoring the need for revised formulations, particularly for large-diameter flexible piles. This study employs a modified Mohr–Coulomb model to comprehensively investigate the load transfer and failure mechanisms of large-diameter flexible piles in sandy soil. An improved formula is proposed to estimate the initial stiffness and ultimate net soil resistance of the p–y curve, addressing the shortcomings of existing design codes that tend to overestimate initial stiffness and underestimate ultimate soil resistance. The results reveal that the initial stiffness of the p–y curve is independent of the pile diameter and the relative compactness, whereas the ultimate soil resistance coefficient increases with the relative density of the sandy soil. Consequently, a hyperbolic function is adopted to characterize the p–y curve, and a new formulation is developed, incorporating the critical role of soil relative density. This proposed p–y formula enhances the prediction accuracy for large-diameter flexible piles under horizontal loading in sandy soil, offering significant advancements in the design of such piles, which are essential for offshore renewable energy projects.