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Research on the Seafloor’s Constructability Properties Supports the Design of Offshore Wind Power

In the future, the construction of offshore wind power will increase exponentially in Finland. The wind energy potential of the Baltic Sea area is 93 GW. In Finland, there is for now only one offshore wind farm, in Tahkoluoto, but there are 1,100 km of coastline, the second largest amount among Baltic Sea countries. The prerequisites for additional offshore wind power construction are therefore good.

In the Geomeasure project, seismo-acoustic surveys are carried out on GTK’s research vessel Geomari. Photo: Juha Rahkonen, © Geological Survey of Finland.

However, many factors affect where wind power can be built, and where it is profitable. The seafloor’s constructability properties play an important role when designing power plant locations and various cable solutions. In addition to the seafloor’s soil type, constructability properties include the quality of the seabed and the thickness of soft sediment layers. The seafloor’s foundation conditions are also affected by water depth, as well as sediment density and strength. The seabed conditions of the Baltic Sea are varied; there are thick and soft sensitive clay areas, and occasional rocky moraines.

The Geomeasure project, funded by the Academy of Finland, aims to investigate the geological layer structure and strength properties of the Baltic Sea seafloor for construction design. The cooperation project is coordinated by Aalto University, with Geological Survey of Finland (GTK) as project partner.

The Geomeasure project includes seismo-acoustic surveys on GTK`s research vessel Geomari, and the undrained shear strength of different sediment layers is studied with free fall cone penetrometer (FF-CPT). In addition, continuous sediment samples are taken from the seafloor reaching a depth of several metres. The samples enable the study of the location and thickness of different geological layers, as well as defining their properties. The geotechnical characteristics of the samples are studied at Aalto University’s research laboratory from parallel samples.

The strength and deformation of bottom sediments are modelled under both static and cyclic loads (the effects of wind, waves and ice). The results are used as baseline information for construction design. They also help to understand the seafloor’s functions when designing the foundation of an offshore wind farm, for example.

In addition to Aalto University and GTK, the project’s management group includes engineering agencies and a wind power production company from Finland. The project’s management group also has international members from the Universities of Southampton and Durham.

During the first field study period of the 3-year project in the summer of 2022, research was conducted in the sea area outside Helsinki, and also outside Pori in the extended area of the Tahkoluoto wind farm. Later, field studies will continue in the Bothnian Bay area.

Undrained shear strength of different sediment layers is studied with free fall cone penetrometer (FF-CPT). Photo: Geological Survey of Finland.

Additional information

Maarit Saresma, Geologist
Geological Survey of Finland GTK
Energy and Construction Solutions, Engineering Geology
maarit.saresma@gtk.fi

Joonas Virtasalo, Senior Scientist
Geological Survey of Finland GTK
Environmental Solutions, Marine Geology
joonas.virtasalo@gtk.fi

Geomeasure

  • Foundations for green offshore energy production in Finland: from marine investigations to the numerical estimation of undrained shear strength of the seabed deposit layers under cycling loading (Geomeasure)
  • The Geomeasure project is a collaboration project with Aalto University (coordinator).
  • The project started at the beginning of 2022 and will continue until the end of 2024.
  • The aim of the project is to deliver information for designing offshore construction and enable the development of easier, faster and more profitable green energy production in the Baltic Sea area.
  • Introduction to the project on GTK`s website: Geomeasure