The response of a plate anchor and embedded mooring in clay to environmental loading: experimental observations and numerical simulations

Plate anchors experience cyclic loads and long-term sustained tension over their design life, leading to the generation and dissipation of excess pore pressure around the anchor and the embedded mooring line, which, in turn, changes the capacity of the anchor–mooring system over time. To explore the effect of this type of loading on the anchor–mooring system response, a series of model scale experiments was conducted in a geotechnical centrifuge, in which different combinations of cyclic loading (mimicking storm events) and sustained loading (mimicking operational loading) were applied to a plate anchor embedded in a normally consolidated clay. Changes in the anchor–mooring system capacity due to this loading were replicated in simulations using a new coupled effective stress macro-element model developed for plate anchors. This new model accounts for the competing effects of strain softening that occur during plate anchor mobilisation and cyclic loading, and hardening due to consolidation, and is shown to reproduce capacity changes measured in the experiments to a very satisfactory level. The paper concludes with example simulations of multi-year time histories of loading established from mooring analyses for a floating wind turbine, demonstrating an alternative to the commonly adopted design approach of decomposing time histories of irregular cyclic loads into a series of cyclic load parcels of uniform amplitude that are ordered by load magnitude.