Mechanisms of anchor chain–clay seabed interaction under cyclic loading considering strength heterogeneity and layer soil profiles

Tensioned mooring systems are widely used for station-keeping of deepwater floating wind turbines, where embedded anchor chains interact continuously with clay seabeds under cyclic loading. This study investigates chain–soil interaction in stratified and heterogeneous seabeds using a Coupled Eulerian–Lagrangian (CEL) large-deformation finite element framework incorporating the Einav–Randolph strain-rate and strain-softening models. The numerical model is validated with analytical expressions through comparisons of fairlead tension and chain configurations. Subsequently, single layer, soft-over-hard and hard-over-soft seabed profiles are analyzed by considering the effects of strength gradient, interlayer strength difference, and layer thickness ratio. Results show that strain-rate effects enhance soil resistance, increasing fairlead inclination and reducing chain embedment and cyclic deformation accumulation. In contrast, strain-softening and sensitivity effects promote strength degradation and plastic deformation. The influence of the linear strength gradient is relatively limited, mainly altering the distribution of disturbance along the depth direction. Interlayer strength difference governs deformation localization and propagation, while layer thickness ratio regulates the interaction range and near-surface response. The findings provide insights into the governing mechanisms of chain–soil interaction and support the reliability assessment of deepwater mooring systems under complex seabed conditions.