Experimental Investigation Into the Influence of a Keying Flap On the Keying Behaviour of Plate Anchors

Plate anchors are used in deep and ultra-deep waters to anchor floating offshore structures. Once installed vertically under the seabed with the aid of a suction follower they must be rotated or “keyed” in order to mobilize full anchor capacity. A keying flap attached to the top of the anchor is commonly used, aiming at reducing the vertical translation component of the installation path during keying, although its efficiency appears to be uncertain. To quantify the performance of this keying flap and to understand its mechanism, centrifuge tests were performed on an anchor model, using Particle Image Velocimetry (PIV) to monitor the trajectory of the anchor and the behaviour of the keying flap through examination of the soil failure mechanism upon keying. Results indicated that the keying flap did not affect the anchor trajectory, except by introducing an offset to the loading.