Objective This study is concerned with the design of monopile foundations for offshore wind turbines (OWTs) in sand. The predictive performance of existing p-y models in large-diameter monopile soil-pile interaction is evaluated. The influence of different factors on the results of these p-y models is discussed.

Method Compared the prediction results of different p-y models for the initial stiffness and ultimate bearing capacity of p-y models under assumed pile foundation dimensions and soil conditions, the influence of sand relative compactness, pile diameter and stress level was discussed. Finally, different p-y models were applied to perform back analysis on the experimental data published in the literature, thereby intuitively evaluating the predictive capabilities of different models.

Result Changes in stress level result in a significant influence on the American Petroleum Institute (API) p-y model. At low stress levels, the API p-y model predicts initial stiffness and ultimate capacity lower than actual values. However, as the stress level increases, the predicted initial stiffness and ultimate capacity tend to be overestimated.

Conclusion For small-scale model tests, the API p-y model provides relatively accurate or conservative predictions. However, for offshore wind turbine monopile foundations under practical stress levels, the API p-y model significantly overestimates the pile-soil interaction stiffness and bearing capacity. Its application to the design of offshore wind turbine monopiles may lead to unsafe results. In contrast, p-y models based on cone penetration test (CPT) data offer more reasonable predictions for both small-scale model tests and large-diameter monopile numerical simulations, showing potential for application in the design of offshore wind turbine monopile foundations.