Anchor Sharing in Sands: Centrifuge Modelling and Soil Element Testing to Characterise Multi-Directional Loadings

Abstract

Offshore foundations are typically designed to resist mooring loads coming from a single direction. This paper provides some insights into the geotechnical challenges associated with anchor sharing (i.e. where mooring loads are coming from multiple directions to one anchor) for Offshore Renewable Energy (ORE) applications. Firstly, the multidirectional mooring load conditions on shared anchors are characterised for cases with one, two and three mooring lines connections. Secondly, multi-directional loadings applied on a caisson foundation in a geotechnical centrifuge facility showed large capacity reduction and large displacement of the foundation at large loading angle. Thirdly, multi-directional simple shear tests have showed that volumetric contraction increases as the degree of shear stress reversal increases. Lastly, the results from the soil element tests are brought into discussion with the physical modelling results to identify the foundation’s response to multi-directional loading.

Optimised design of screw anchors in tension in sand for renewable energy applications

“…compression/tension load, of the order of 10-20MN). Wave energy converters vary in size, but the largest may require a vertical capacity of several MN (Gaudin and O'Loughlin, 2018;Herduin et al, 2018) due to the inclination of taut mooring lines or consist of a single point absorbed with a single vertical mooring line (Vicente et al, 2013a). In contrast, floating net-cage systems used in aquaculture also require an engineered anchoring solution for offshore deployment in exposed waters (Huang et al, 2008), although typically of a lower order of magnitude (~0.2MN).…”