The Geotechnical Design Reliability of Offshore Wind Monopiles

Abstract Offshore wind energy is expected to become one of the major clean energy sources to combat climate change. Monopile foundations play a central role in shallow water offshore wind development. The design of the monopile is gradually matured but the long-term reliability level of monopile foundations against the catastrophic failure remains largely unclear. Thus, the objectives for the current study are (1) to incorporate both loading and resistance randomness in the reliability calculation to obtain a general sense of the safety levels of offshore wind monopile foundations and (2) to identify the key parameters affecting the reliability levels of monopile foundations. The monopile is designed based on 100-year extreme loads following American Petroleum Institute guidelines. Probabilistic analyzes are performed within the framework of the first-order reliability method. The annual failure probability of monopile foundations in the ultimate limit state is estimated. The study shows that the long-term uncertainties in the mean wind speed and the maximum significant wave height dominate the reliability level. The effect of the uncertainty in the breaking wave force is not as significant as commonly perceived, and the reliability level is insensitive to the uncertainties in the geotechnical parameters.