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 Compare the predictions of different p-y models for initial stiffness and ultimate capacity under assumed pile size and soil conditions, discussing the effects of sand relative density, pile diameter, and stress level. Finally, perform back analysis on test data published in the literature with different p-y models to visually evaluate the predictive capabilities of each model.

Result Changes in stress level result in a significant influence on the 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 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.