Numerical study on the effects of scour on monopile foundations for Offshore Wind Turbines: The case of Robin Rigg wind farm. Issue 167 (April 2023)

• Record Type: Journal Article
• Authors: Menéndez-Vicente, Carlos; López-Querol, Susana; Bhattacharya, Subhamoy; Simons, Richard
• Is Part Of: Soil dynamics and earthquake engineering. Issue 167(2023)
• Publication Date: 2023-04
• Subjects: Scour -- Monopile foundations -- Offshore Wind Turbines -- Soil structure interaction -- Natural frequency -- Finite elements analysis; Soil dynamics -- Periodicals; Earthquake engineering -- Periodicals; Sols -- Dynamique -- Périodiques; Génie parasismique -- Périodiques; 624.176205
• DOI: 10.1016/j.soildyn.2023.107803
• Languages: English
• ISSNs: 0267-7261

Abstract

Abstract: Scour around monopiles supporting Offshore Wind Turbines (OWT) may cause a significant reduction in the foundation capacity and the natural frequencies of the soil–structure system. The decommission of two monopiles at the Robin Rigg wind farm after only six years of operation due to massive unexpected scour demonstrates the hazard that an active marine environment poses to OWT. Assessing and predicting the quantitative impact of scour on monopile foundations from a point of view of the utilisation of the foundation capacity is hence crucial to its long-term structural and operational safety. Using finite element analysis, the present study quantifies the influence of scour through moment M and lateral load H ( M − H ) interaction curves and Load Utilisation (LU) ratios. It analyses the first and second natural frequencies of OWT exposed to different scour morphologies. This methodology is applied to a large-diameter monopile embedded in sand and to the scour-induced failed foundation of the Robin Rigg wind farm. The results indicate that, with increasing scour depth, the M − H capacity and the natural frequencies are reduced due to the loss of lateral confinement. The response of the system is found to depend on the rigidity of the pile governed by the slenderness ratio, the capacity of the soil to redistribute loads with increasing scour, and the effects of overburden pressure on deeper unscoured soil layers. The LU methodology has proven to be an appropriate and efficient approach to predict the long-term performance of scoured monopiles. Highlights: Scour affects the static capacity and the natural frequencies of monopile foundations. M − H interaction curves were obtained using finite element analysis. Load Utilisation ratios were used to predict the capacity of scoured monopiles. The methodology was applied to the failed foundation at the Robin Rigg wind farm.