The best wind locations can be found at the edges of the land: the sea dikes in The Netherlands. Sea dikes can be considered as un-orthodox locations. The Oostpolderdijk wind farm project is the first project were wind turbines are located on top of a primary sea dike.
The North of the Netherlands is an earthquake area, what makes this project extra challenging. The soil that is found underneath the location is sensitive for vibrations. Extra-ordinary projects ask for extra-ordinary solutions. Where 99% of the wind turbine foundations in the Netherlands are piled foundations due to the weak soils, we chose to make shallow foundations for this project. The two main reasons to do so are:
1. A piled foundation would mean the introduction of a rigid element in the sea dike. This would cause a danger for vaults in the soil next to the foundations and therefore possible leakage through the dike. A shallow foundation will deform with the deformations of the dike.
2. A piled foundation will easily transfer the vibrations of the wind turbine to the sensitive soil layers and may cause liquefaction of these soil layers. A shallow foundation will distribute the vibrations and therefore liquefaction can be avoided.
A point of attention is the deformation of the foundations. The tilt of the tower should stay within the acceptable limits. This requires state-of-the-art design models and the development of new guide lines for this area. The combination of knowledge of dike safety and wind turbine foundations make innovations possible.
The concrete foundation structure is modeled using full physical non-linear 3D modelling: a design method used by Windbase for many years now. This will give us the opportunity to get a good insight in the “real” behavior of the concrete structure and to optimize reinforcement.