Centrifuge Modeling of the Monotonic Capacity of Offshore Ring Anchors in Sand-Article

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The study used 70g centrifuge tests to examine the monotonic tensile capacity of ring anchors embedded in dense, saturated sand. Eight tests compared two embedment depths (3D and 6D) and four loading angles, measured from horizontal.<br /><br />Anchor capacity increased with both embedment depth and more horizontal loading. At 30° from horizontal, capacity was three to four times that under vertical loading. Deeply embedded anchors carried 2.6 times the shallow-anchor capacity at 30° and 1.8 times the capacity under vertical loading. The findings reflect greater mobilization of lateral soil resistance under near-horizontal loading, as well as changes in failure mechanism with depth: shallow anchors formed a failure wedge reaching the ground surface, while deeper anchors mobilized soil flowing around the anchor.<br /><br />Anchor movement was not perfectly aligned with the applied load, but deviations were small. Anchors initially moved relatively more horizontally and, after peak load, relatively more vertically. Installation also disturbed the surrounding sand substantially: CPT-based estimates indicated local relative density fell from about 79% to below 20% in the affected zone. This disturbance was especially relevant to vertical capacity.<br /><br />The results highlight the importance of accounting for loading direction, embedment, and installation effects when designing ring anchors for floating offshore wind systems. Further field testing is needed to determine whether similar installation-induced soil loosening occurs at full scale.

Keywords

ring anchors

monotonic tensile capacity

dense saturated sand

centrifuge tests

embedment depth

loading angle

horizontal loading

soil resistance

failure mechanism

offshore wind foundations