Numerical Assessment of Scour Effects on the Ultimate Bearing Capacity of Rigid Helical Anchors in Clay Seabeds

Helical anchors represent a promising solution for anchor systems of floating offshore wind turbines, yet scour-induced changes to the seabed threaten anchor stability. The bearing capacity and failure mechanisms of helical anchors under such conditions have not been fully investigated. Finite element (FE) analyses examine scour geometry, anchor length, and soil heterogeneity (κ = kD/sum, where k is the undrained strength gradient, D is the shaft diameter, and sum is the surface strength). The results demonstrate that scour depth is the dominant factor governing bearing capacity, whereas scour width and slope angle have limited effects. Horizontal capacity is particularly sensitive to scour because the corresponding failure mechanism develops mainly within shallow soil. Increasing κ mitigates scour-induced capacity loss, with this effect being most pronounced as κ rises from 0 to 2, beyond which further increases yield diminishing benefit. Across different helical anchor embedment lengths, scour is shown to shift the critical embedment depth separating shallow and deep failure mechanisms, particularly under low soil heterogeneity. The effects of loading direction are further evaluated within the V-H loading space. Finally, predictive expressions are developed to capture the coupled effects of scour geometry, soil heterogeneity, and anchor length for engineering capacity assessment.