Seismic performance of large-scale OWT monopiles in liquefiable soils: A numerical study and analytical relationships

The paper presents the results of an extensive parametric study on the effects of earthquake-induced liquefaction on the response of monopile-supported Offshore Wind Turbines (OWTs) with capacity up to 15 MW. For this purpose, an advanced 3D numerical methodology is developed that takes into account the complex interaction mechanisms between the liquefied soil, the foundation and the superstructure, using state-of-the-art numerical features, validated against experimental data. In total, more than 700 analyses are performed considering all critical parameters affecting the problem, including the capacity of the OWT, the magnitude of the environmental loads, the soil and the foundation properties, and the intensity of the seismic motion. The results of the analyses are further processed and simplified expressions are proposed for the preliminary Front-End-Engineering-Design (FEED) of the OWT performance. Finally, it is shown that various schemes applied to provide scour protection to the monopile foundation can significantly benefit the OWT performance.