Numerical study on the yield surface of plate anchors in clay: Effect of soil-anchor interface tension

The growing demand for floating offshore wind turbines in deep-water environments has increased reliance on plate anchors to provide holding capacity. These anchors are subjected to combined normal, sliding, and rotational moment loadings during drag-in installation, keying processes, and long-term service as permanent mooring systems. Most previous studies have evaluated the combined loading capacity yield surface of plate anchors by assuming a fully bonded soil-anchor interface, equivalent to infinite interface tension – an assumption that may be unconservative. This study investigates the uniaxial bearing capacities and combined loading yield surfaces of plate anchors in clay under varying soil-anchor interface tension conditions using finite element modelling. A comprehensive parametric study was performed, considering embedment depth, anchor thickness ratio, anchor roughness, and, critically, soil-anchor interface tension. The results show that the yield surface evolves disproportionately in three-dimensional loading space, with pronounced enlargement in the normal direction as interface tension increases, until a critical value is reached. Parameterised design equations are proposed for the yield surface, enabling straightforward evaluation of combined loading capacities under varying interface tension conditions.