Scour Geometry and Its Implications for Monopile Bearing Performance: A State-of-the-Art Review

The rapid upscaling of offshore wind turbines has made local scour around monopile foundations a critical concern for foundation capacity and long-term service safety. This state-of-the-art review examines local scour geometry and its implications for monopile bearing performance. Drawing predominantly on the literature published between 1990 and 2026, the review systematically evaluates the influence of foundation dimensions, wave–current conditions, and seabed properties on scour development, and critically assesses key geometric parameters—including maximum scour depth, width, side slope angle, volume, and three-dimensional morphology—for their representation of soil loss and use in current engineering practice. The applicability and limitations of physical experiments, empirical methods, numerical simulations, and field monitoring are compared. The mechanistic linkage between scour geometry and bearing response is elucidated through stress-path alterations, soil confinement degradation, and geometric interactions, with effects on lateral capacity, cyclic response, and natural frequency analyzed. The findings demonstrate that maximum scour depth alone is insufficient; reliable assessment requires multi-parameter characterization incorporating width, slope, volume, and 3D morphology. Distinct from existing reviews focused on prediction or monitoring, this review contributes a systematic elucidation of the mechanistic pathways—soil removal, stress unloading with confinement degradation, and stiffness migration—through which geometry affects bearing performance, and proposes standardized reporting protocols. Future research priorities include addressing scale effects for large-diameter monopiles, advancing long-term 3D monitoring, and developing coupled hydrodynamic–geotechnical frameworks. This review offers a structured reference for researchers and practitioners in scour assessment and foundation design.