The Wikinger offshore wind farm (OWF) is situated in the German Baltic Sea comprising seventy 5MW wind turbine generators. Each turbine is supported by a four legged jacket structure founded on driven steel piles. Ground conditions over much of the project area are dominated by thick Chalk layers overlain by Glacial Till. A review of pile design methods for Chalk and related onshore pile test campaigns highlighted significant design uncertainties which led to the client’s decision to conduct dynamic and static offshore pile tests at the Wikinger site. It was the first time static pile load tests of such scale and depths were executed underwater for an offshore wind farm project. Without the site specific tests the design uncertainties would have likely resulted in overly conservative designs for the vast majority of the piles.
GCG provided independent advice, technical design and tender review as well as optimisation for the large scale offshore pile testing campaign. This work was completed together with Prof Richard Jardine who is a leading expert in offshore geotechnics and pile design and a long standing Associate of GCG. The results from the pile testing led to significant economies in the pile design. Direct benefits included an aggregate reduction in pile length of around 3 km which led to large savings in material, fabrication, installation and CO2 emission costs. Considering also the numerous indirect benefits, the gains from the pile testing campaign greatly outweighed its costs.
In further phases of work, GCG was retained to undertake independent analysis of the field Dynamic Load Testing (DLT) using wave matching techniques to quantify the pile capacity with a number of methods, including advanced methods more commonly employed in research.
The pile testing was critical to obtain Innovate UK funding for a 3 year Joint Industry Program between Scottish Power, Imperial College London and GCG to improve pile design methods in Chalk. This work is being continued by the Engineering and Physical Sciences Research Council (EPSRC) funded ALPACA project, with broad industry support, for which GCG is providing some funds and is represented on the Steering Committee.
Barbosa, P., Geduhn, M., Jardine, R.J. & Schroeder, F.C. (2017). Large scale offshore static pile tests – practicality and benefits. 8th Int. Conf. on Offshore Site Investigation and Geotechnics – OSIG 8
Buckley, R. M., Kontoe, S., Jardine, R. J., Maron, M., Schroeder, F. C. & Barbosa, P. (2017). Common pitfalls of pile driving resistance analysis – a case study of the Wikinger Offshore Windfarm. 8th Int. Conf. on Offshore Site Investigation and Geotechnics – OSIG 8
Barbosa, P., Geduhn, M., Jardine, R.J., Schroeder, F.C. & Horn, M. (2015). Full scale offshore verification of axial pile design in chalk. Proc. Int. Symp. Frontiers in Offshore Geotechnics – ISFOG 2015, Oslo (Ed. V. Meyer)