Seismic_on_Piles: Monitoring soil properties on offshore structures

At a glance

• The subsoil of offshore wind turbines is subject to changes over time caused by the installation and operation of the turbines.
• These changes, in turn, influence the offshore wind turbine and its operation, right up to its stability, and must therefore be recorded.
• The methods applied to date include dynamic pile measurements and direct outcrops in the vicinity of the piles.
• In the Seismic_on_Piles research project, Fraunhofer IWES is developing a new, more cost-effective investigation method based on repeated seismic measurements over a longer period of time.

The challenge

The soil around an offshore wind turbine’s foundation structure can undergo changes during the installation of the turbine and its operation. These installation and set-up effects have a lasting impact on the construction and operation of the turbine and can even influence its stability. As such, they need to be identified and quantified on a continuous basis.

The standard methods for this are dynamic pile measurements and direct outcrops in the vicinity of the piles, which record snapshots of these changes and make it possible to derive trends.

The solution

In the Seismic_on_Piles research project, Fraunhofer IWES develops a new investigation method that enables cost effective monitoring of the foundation soil with repeated seismic measurements over a longer period of time. The so-called 4D seismics is already an established method for monitoring measurements and measurements of temporal changes in the oil industry but has not been applied in the offshore wind industry with its far smaller-scale problems so far.

During the project, the scientists will measure changes in the subsoil using seismic methods in large-scale tests under offshore-like conditions in the test facilities of the Test Center for Support Structures Hannover (TTH) and monitor further subsoil changes. All the tests will be accompanied by numerical models and simulations allowing virtual mapping and scaling of the results. This will provide a calibration basis for the altered subsoil properties and their effects on the wind turbine’s support structure.

The added value

The results of the geotechnical, structural-mechanical, and geophysical measurements will subsequently be incorporated into partial models of a comprehensive 3D subsoil model. This will result in a reliable and cost-effective monitoring procedure for recording time-dependent subsoil parameters in the vicinity of the pile and could additionally be used to assess the subsequent use of wind farm areas.