Out of plane loading of drag embedment anchors for floating renewable energy technologies

Drag embedment anchors are a technology that has developed through many years’ experience. However, as demand increases for anchoring of clean energy technologies offshore, so the requirements of modern drag embedment anchors have evolved. A more resilient infrastructure requires improved understanding of how an anchor will perform in abnormal loading conditions, such as when a load is applied out of plane to the direction in which it was installed. This work presents data from a set of tests carried out on the University of Dundee geotechnical centrifuge in order to understand how a typical 12t Bruce GP drag embedment anchor performs in sandy soil. Initial tests in loose and medium-dense soil conditions identify the ultimate holding capacity (UHC) of the anchor. Subsequent tests were then conducted in which the anchors were dragged to 60% of the UHC, to mimic current installation practice, before being loaded to failure at angles of 20, 30 and 45°, inclined to the in-line direction. Measurements of the out-of-plane holding capacity were compared to the in-line loading conditions and demonstrated that holding capacities under side-loading angles up to 20° were similar to the straight pull capacity.