Experimental Investigation and Numerical Analysis of the Behaviour of Plate Anchor Foundations Subjected to Cyclic Loading in Sands

EPRSC Project Description
Experimental Investigation and Numerical Analysis of the Behaviour of Plate Anchor Foundations Subjected to Cyclic Loading in Sands

Over the past several decades, offshore wind farms have been undergoing significant development and expansion in terms of their power capacity and operating regions. While most of the offshore wind turbine (OWT) structures are supported by fixed foundations (e.g. monopile, jacket foundations, etc.), alternative foundation types have been investigated as options that are more suitable to large OWTs and deeper waters. Specifically, plate anchor foundations have been considered a feasible and efficient foundation type for applications in floating OWTs with mooring systems [1], [2].
Foundations of floating OWTs are subjected to a combination of uplift and horizontal loads, which are induced by the environmental loads acting on the OWT structure and mooring lines. Due to the cyclic nature of the loads, the foundation is subjected to a significant number of loading-unloading cycles during its service lifetime [3]. Although relatively limited, several experimental studies have been carried out to investigate the behaviour and capacity of plate anchors under cyclic loading. Overall, the studies showed consistent results, where the cyclic loading results in an increase in the foundation capacity in both silt [4] and sands [5], [6]. While the change in the foundation capacity has been simulated on a theoretical basis for silts [4], there has been limited analysis on the methods for quantifying the capacity change of plate foundations in sands.
Thus, this research project aims to investigate the response of plate anchor foundations subjected to cyclic loading in sands. In addition, it is aimed to develop analytical and numerical models for predicting the effects of cyclic loading on the foundation capacity. The consideration of the strength gain effects due to cyclic loading would allow for more optimal and economic foundation design solutions for offshore applications. This project falls within the EPSRC "Engineering" research area, within the context of the "Energy and Decarbonisation" theme.
For this project, a series of laboratory tests will be carried out to investigate the behaviour of plate foundation models under loading-unloading cycles in saturated sand. The foundation models will be subjected to cyclic loading with different frequencies and magnitudes. The effects of the loading characteristics on the foundation capacity and behaviour will be analysed and quantified. Based on the analysed mechanism behind the foundation behaviour after cyclic loading, an original analytical model will be suggested for the prediction of the post-cyclic monotonic capacity. In addition, three-dimensional finite element analysis (FEA) will be carried out for the numerical simulation and parametric studies on the foundation behaviour. Based on the results of the parametric studies, optimal design parameter values would be suggested for the maximisation of the post-cyclic foundation capacity. Finally, a general design framework for plate foundations of OWTs will be newly suggested by incorporating the developed analytical models for estimating the post-cyclic monotonic capacity or the FEA model.