Posters

Abstract

Onshore wind continues to increase its contribution to the renewable-energy-mix every year. One of the main international standards, where also the requirements for foundations are set, is IEC 61400. When shallow foundations are designed, the requirement of the standard is that during a normal operation load case, the foundation must always be in contact with the soil with all its surface. Only the latest edition of IEC 61400 relaxed the requirement, but due to the nature of repetitive wind loads, a verification of the soils susceptibility for cyclic degradation must be performed. The verification requires extensive and costly soil testing methods, which not always available. Therefore, the onshore foundation design industry is still mostly following a conservative path and keeping the foundation in contact with the soil during the operational load case. One of the methods to reduce the foundation size and satisfy the above-mentioned requirement, is to use not a disc-shaped but a ring-shaped contact area of a foundation. In practice, instead of building the more complicated ring-shaped foundation, often a compressible layer under a standard disc-shaped foundation is used. The compressible layer is chosen such, that the loads could be redistributed to the ring-shaped area.  In this article, the usefulness of such a compressible middle area under a shallow foundation of a wind turbine to reduce the foundation size is investigated by the means of numerical modelling. Different soil constitutive material models are used, and differences in the results discussed.