A unified "p-y+M-θ " model for laterally loaded piles considering rigidities of various piles

The large-diameter monopiles account for over 70% in construction of offshore wind turbines in China. The current p-y curve design method is primarily suitable for the small-diameter flexible piles. It has long been recognized that the method is inadequate to describe the lateral behavior of large-diameter monopiles, due to the ignorance of the soil resistances arising from base shear and base moment, which becomes more pronounced as the pile rigidity increases. Consequently, it will significantly underestimate the deformation and capacity of the semi-rigid and rigid piles (commonly used in offshore wind projects in China and Europe, respectively), bringing challenges for cost reduction. In light of these issues, the authors have proposed a "p-y+M-θ"model that aims to reasonably predict the lateral monotonic response of monopiles with a broad coverage of rigidities (or length-over-diameter ratios) in a unified way. An extension of the model is then made to enable the capability for predicting the cumulative lateral behavior under cyclic loadings. With the proposed "p-y+M-θ"model, the authors are invited by the Organizing Committee of 4th International Symposium on Offshore Geotechnical Engineering (ISFOG-2020) to participate in a blind Class-A prediction event, where the experimental data are generated from the centrifuge tests performed by University of Western Australia (UWA) on piles in soft clay under lateral monotonic and cyclic loadings. The results of some element tests for the same clay as used in the centrifuge tests are provided ahead of the Class-A prediction event, for calibrating the model parameters. All the measured responses of lateral piles under monotonic and cyclic loadings are found to be reasonably reproduced by the proposed "p-y+M-θ"model. Compared to the predictive capability of the other 28 models used by the parallel international teams participating in the prediction event, the "p-y+M-θ"model shows a leading performance in the context of monotonic and cyclic predictions. The proposed "p-y+M-θ"model constitutes an advantageous and simple alternative to the design of monopiles under lateral loads.