The Borkum West II offshore wind farm is being developed in the North Sea, approximately 45km offshore northern Germany. The first phase of the project includes the construction of 40 No. 5MW turbines. The turbine hub height is approximately 90m above sea level, and the rotor diameter is 116m. The turbines are in water depths of approximately 30m, supported by tripod structures on driven pile foundations.
GCG were engaged to undertake an independent geotechnical design review for the pile foundations to support the technical due diligence process for the project. This developed into a collaborative design process aimed at identifying and mitigating geotechnical risks and developing the foundation design methodology for the project. The design review considered the site investigations and interpretation, pile installation and driveability, static axial and lateral pile capacity, storm loading characterisation, and the effects of cyclic loading on pile axial capacity and lateral loading response. A pile driving risk assessment was developed to evaluate and mitigate the risks of pile buckling during driving at each turbine location. The pile design was based on the ICP method, coupled with analysis of the effects of cyclic lateral and axial loading on the axial pile capacity. Various design codes were also evaluated to compare the effects on the design pile lengths. The geotechnical design review performed by GCG resulted in an agreed and validated pile design methodology that was accepted by the project’s funders and the certifying authority, reduced risks during pile driving in dense sands, and also achieved substantial cost savings through optimisation and refinement of the pile designs.
Merritt, A. S., Schroeder, F. C., Jardine, R. J., Stuyts, B., Cathie, D. & Cleverly, W. (2012). Development of pile design methodology for an offshore wind farm in the North Sea. 7th Int. Conf. on Offshore Site Investigation and Geotechnics, London.