Gravity Based Foundations for Offshore Wind Turbines: Cyclic Loading and Liquefaction

Abstract

In current modelling of excess pore pressures (EPPs) below marine structures, the irregular nature of cyclic loads and the real storm development are not taken into account. The effect of the irregular cyclic loading in time is investigated in this paper. The wind, wave and turbine loads on a gravity based foundation (GBF) are derived in the frequency domain. The real storm development is based on the CoastDat dataset. The load input is used in a program which takes the generation and dissipation of pore pressures under cyclic loading into account. Also, densification is included. The results show that the first storm in the lifetime of the GBF results in the highest EPPs. The EPP decreases in time, due to significant dissipation and densification during the build-up of a storm. Therefore, not the storms with the largest cyclic loads but the storms with the fastest build-up result in the highest EPPs, since this limits the process of densification. A large scatter is found in the maximum values of EPPs due to the irregular nature of the loads.