Assessment of soil conditions

The reflected sound signals are recorded by a total of 60 hydrophones inside the streamer.

Multi-channel seismic profiles

Simple-shear cell

Exact knowledge of local construction site conditions is an important prerequisite for the planning and development of offshore wind farms. This is the basis for the choice and optimal dimensioning of wind energy turbine support structures. As the foundation work costs have a comparatively large share of the total offshore wind energy turbine costs this area has a great cost optimization potential.

Established investigation methods such as geological drilling and penetration tests deliver important foundation-relevant information, however, they are limited to the respective test sites. Using these methods it is only partially possible to gain information on construction site conditions in the surrounding areas; this can be inadequate and especially for foundation structures such as ackets or tripods.

In contrast, geophysical methods give an extensive, comparatively fast and cost effective overview of the foundation conditions, however, they do not allow direct statements to be made concerning foundation characteristics. One of the aims of the Offshore Site Assessment, Ground group to consider the subject of foundation assessment holistically and to usefully and effectively apply the different methods in relation to each other.

In the geophysics field Fraunhofer IWES has developed a multi-channel seismic measuring process which is particularly tailored to offshore wind energy requirements. Common problems in conventional measuring processes such as inadequate signal penetration and the bad mapping of complex structures have been overcome. We have successfully conducted geophysical surveys for several customers for offshore wind farms with this method. The results show unprevailed resolution and signal penetration in the characterisation of subsoil conditions for offshore wind farms.

Regarding geotechnical offshore foundation structure dimensioning, the working group offers in-situ surveying methods (CPT) and geotechnical as well as both monotone and cyclical laboratory testing in order to characterize sea-bed samples. The parameters gained here are the basis for assessment and the foundation construction dimensioning process. The assessment is carried out pursuant to BSH standards, encompasses cyclic loading and is, according to client’s wishes and requirements, supported and safeguarded through implementing FE procedures.


Data sheet "Geophysical Site Investigation"

Publications

2015

Innovative measurement technologies for met-ocean and soil conditions
Lange, Bernhard; Gottschall, Julia; Rudolph, Claudia; Wolken-Möhlmann, Gerrit; Viergutz, Thomas; Meier, Florian; Spieß, Volkhard
(Presentation)

12th Deep Sea Offshore Wind R&D Conference, EERA DeepWind2015
Feb. 4-6, 2015, Trondheim, Norwegen
zu Fraunhofer Publica


Potential of estimating relative density by measuring shear wave velocity in field and in laboratory
Biryaltseva, T.; Kreiter, S.; Mörz, T.; Lunne, T.
(Presentation)

Proceedings of the Third International Symposium on Frontiers in Offshore Geotechnics, ISFOG 2015, Vol.2, S.1037-1042
June 10-12, 2015, Oslo, Norwegen
zu Fraunhofer Publica