Long-term degradation of monopile lateral capacity due to seabed scour: A field data-informed numerical study

Although scour is widely recognized as a key design consideration, its underlying mechanisms and temporal evolution remain insufficiently understood due to a scarcity of long-term field monitoring data. Consequently, the effects of scour on foundation stiffness and lateral capacity have yet to be fully quantified. This study analyzes six years of annual scour inspection data from a representative offshore wind farm consisting of 54 monopile-supported turbines. Based on this unique full-scale dataset, empirical models are established to describe the temporal evolution of key scour geometry parameters: maximum scour depth (MSD), maximum scour extension (MSE), and scour slope angle (SSA). These parameters follow power-law trends-MSD and MSE increase over time, while SSA decreases. The empirical relationships further inform a three-dimensional finite element modeling framework incorporating the advanced SANISAND-MS constitutive soil model. Simulation results indicate that after 30 years of scour development, the initial lateral foundation stiffness is reduced by approximately 20.5%, and the ultimate lateral capacity declines by about 14%, accompanied by a notable decrease in lateral soil resistance. By validating established scour trends with unprecedented field evidence, this study provides a transferable methodology that integrates monitoring data and numerical simulation to support the design and protection of offshore wind foundations.