Experimental investigation on the mechanical response of clay under cyclic loading conditions relevant to shared anchors

As offshore wind energy ventures into deeper waters, floating offshore wind technology has emerged as a critical area of research. However, high cost remains a major barrier to the development of this sector. The implementation of shared anchoring systems in large-scale floating wind arrays presents a promising solution for cost saving by reducing the number of anchors. However, such configurations introduce complex loading patterns on shared anchors due to phase differences in mooring line tensions and misalignment of environmental elements (wind, waves, currents), resulting in multidirectional cyclic loading on the anchors with resultant direction varying over an angular range. To characterise the clay behaviour under this unique cyclic loading condition, the authors conducted 25 biaxial cyclic direct simple shear tests with elliptical shear stress paths in the x–y plane. The tests revealed that the presence of the minor cyclic shear stress drastically accelerates the degradation of the soil under undrained cyclic loading. Building on these findings, an equivalent cyclic shear stress parameter is proposed that quantifies the effect of multidirectional loading. This novel parameter enables the adaptation of conventional cyclic contour diagrams, which are well established in offshore geotechnical practice, to predict soil response under elliptical shear stress paths. The methodology offers practical advantages for shared anchor design, allowing engineers to leverage existing cyclic design frameworks while accounting for complex loading scenarios through stress path transformation.