Comparison of the behaviour of a drag embedment anchor using 1-g and centrifuge scale model testing

Offshore wind power cable failure currently accounts for the majority of the cost associated with insurance claims for offshore wind projects. Faults that occur typically take 100+ days to repair during which time energy is not being transmitted to the electricity grid. The most effective method for protecting the export cables from fishing and anchor related damage is to bury them in the seabed, but current guidance on how deep they should be buried is ambiguous. There are a number of variables that influence the penetration of anchors, such as the anchor size (typically considered as a mass of the anchor), the fluke length, fluke angle (or opening angle) and the soil type into which the anchor is being deployed. The fluke length and the angle vary depending on the anchor size, the anchor type (fixed or flipper style) and the manufacturer of the anchor (the same anchor from different manufacturers can have slightly varying dimensions). Current industrial guidance suggests that an anchor’s penetration behaviour can be predicted based upon its fluke length, the vessel displacement and the soil type but this does not consider the physical properties of the soil or the overall geometry of the anchor. In this paper a comparison of the penetration behaviour of a Class F (AC-14) anchor has been investigated in loose soil using centrifuge and 1-g model scale testing. The results indicate that the 1-g testing is able to match the behaviour of the anchor testing in the centrifuge in terms of both the position of the anchor and its orientation during the dragging event.