Combined study of the geological and geotechnical measurements of fine-grained sediments at a planned offshore wind farm extension area in Finland

Abstract

Offshore renewable energy production is increasing rapidly in Finland. Most of the planned offshore renewable energy, particularly offshore wind farms are located in western Finnish waters relatively close to the coast. Shallow water enables optimization of the location of the wind turbine foundations however the ground conditions can change quickly because of the complex glacial and post-glacial sediment cover. Knowledge of the geological and geotechnical properties of the subsurface sediments contributes to safe and cost-effective design of offshore structures. This study focuses on analyzing the geological and geotechnical variability of the fine-grained sediments at a planned offshore wind farm extension area in western Finland. The sediments and their geotechnical properties in the study site vary in depth and character on a comparably small scale depending on their depositional environment. The main geological characteristics play an important role while interpreting the geotechnical properties, e.g., soil undrained shear strength. The study shows seismoacoustic sub-bottom profiles combined with geological and geotechnical index properties from sediment coring supplemented by dynamic undrained shear strength from free fall cone penetrometer (FFCPT) tests. FFCPT tests can successfully identify sediment units and support sub-bottom profile interpretation. Ground-truthing the actual shear strength values from the FFCPT by laboratory soil testing is discussed. This research is part of the Geomeasure project, funded by the Research Council of Finland (Grant No. 347602).