Drained monotonic and cyclic capacity of a dynamically installed plate anchor in sand

Abstract

The emergence of commercial offshore floating renewable energy devices that are expected to be deployed in large integrated arrays in relatively shallow water requires anchor types that are suited to sandy seabeds. This paper considers centrifuge test data that quantify the capacity of a novel dynamically installed plate anchor in sand under drained monotonic and cyclic loading. The monotonic tests investigated the role of the eccentricity of the load attachment point from the plate, the mooring line load inclination at the seabed and the plate embedment depth, whereas the cyclic tests examined the capacity mobilisation due to both regular and irregular drained cyclic loading for a fixed embedment depth and seabed load inclination. The test data indicate that an optimal anchor design would employ a load attachment point that is eccentric from the plate by at least 0.6 times the plate height, and that the anchor provides higher capacity when the seabed load inclination is horizontal (catenary mooring) than when it is vertical (vertical taut mooring). The centrifuge data show that drained cyclic loading does not degrade anchor capacity, and may be beneficial provided the cyclic loading involves a history of lower level cyclic loading that densifies the sand.