Optimum In Situ and Laboratory Geo-Testing for Offshore Wind Turbines

Offentlig prosjektsammendrag

Offshore wind turbines differ significantly from the large offshore installations for the exploitation of oil and gas: the foundations for wind turbines on a wind energy farm are small in base area, many turbines are to be installed over a large area, there is usually very limited site-specific geotechnical data available at the location of each turbine, the loads system imposed by the wind, current and sea waves are much more complex. Because the areas of the foundations are small, and because of the complex combination of loads transferred to the soil via the turbine, there is also possibility of partial drainage during the one cycle of loading due to waves, wind and current. For design, one needs to select representative soil parameters for each wind turbines over this wide area of several km2, without being too conservative either, otherwise the solutions become too expensive. The selection of the soil parameters becomes very challenging because of the novelty and uncertainties involced. This project aims at developing a Geotechnical Design Tool for Offshore Wind turbines (OWT) based on generic laboratory testing programs and optimised in situ testing programs with the cone penetration test (CPT). Three aspects are prioritized: an "optimum" generic laboratory test program for OWT; a CPT-based "Geotechnical Design Basis" (GDB) for OWT, with expected soil conditions over a site and calibrated cone resistance factor to reduce the variation in soil properties; and a Geotechnical Design Tool (GDT) for offshore wind turbines on the basis of CPT and laboratory tests. The approaches will be verified with one case study in the North Sea.