Geotechnical performance of a novel gravity base type shallow foundation for offshore wind turbines

This paper presents a novel foundation solution specially developed for offshore wind turbines installed on sandy or stiff soils. It is a pre-fabricated cross-shaped structure which rests on the seabed through four skirted plates. The geotechnical performance of the foundation has been analysed numerically with respect to both capacity and displacement during extreme loading and normal operation. The effects of different geometrical aspects such as skirt length and structural stiffness have been studied by means of 2D and 3D Finite Element simulations. Fully coupled stress equilibrium and pore water flow simulations have been performed in order to analyse the influence of accumulated excess pore pressure due to cyclic loading. The long-term behaviour of the foundation is discussed based on stability and failure considerations. The results of the numerical study show that the proposed foundation solution offers a viable alternative as a safe foundation for offshore wind turbines. This has been demonstrated representatively for a 5 MW wind turbine installed in a water depth of 35 m on homogeneous ground subjected to the governing design load cases.