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Case Study: Offshore In The German Bight

Updated: Oct 11

We open the Geotechnics archive to discover what some of our Engineers were up to in Autumn 2011, over a decade ago!

We were approached by Osiris Projects to assist them in completing an offshore survey for a number of windfarm interconnector cable routes in the German Bight for TenneT Offshore GmbH, the leading electricity transmission system operator in the European Union. Geotechnics was to supply geotechnical engineers aboard the MV Poseidon to carry out logging, sampling and in situ testing during vibrocore operations and our team of engineers rose to the challenge.

Working as part of a multi-disciplinary international team, a total of 351 exploratory hole locations along 13 cable routes within a 25,000km² area off the west coast of Germany were investigated. The sampling was carried out using the Osiris’s newly purchased GeoCorer 6000 Vibrocorer.

The vibrocore locations were drilled approximately every kilometre along the proposed routes, or at areas of interest highlighted by previous geophysical surveys. The vibrocorer was lowered by a winch from the A-frame located at the stern of the ship and winched to the seabed, where the coring commenced. Once the full depth of penetration or refusal was achieved the corer was brought back to the surface. Each sample was drilled using a 6m length barrel and sample recovery varied from 3m up to 6m. Back on deck, the sample liner was extracted from the barrel.

Onboard, our geologists cut each tube into 1m segments, carried out thermal resistivity testing, preliminary logging and then sealed and labelled each tube ready for transportation to our facility in Chester.

There, each 1m sub-sample tube was opened up longitudinally in two parallel lines using a power cutter on a bench that was specially constructed to hold the sample whilst undertaking this tricky task. The sample was then photographed within a lined enclosure which gave uniformity of lighting and photographing distance and logged in detail. Following this exercise specimens were selected from each sample and sent to our UKAS accredited laboratory in Coventry for particle size distribution and other classification tests.

The Specification required that test procedures complied with the German DIN Standards and hence procedures for doing so were devised, after appropriate translation, and software programming. Tests were done in the Company’s Special Testing laboratory by designated staff.

The project required flexibility by the staff to adapt to conditions off-shore and the vagaries of the weather in this moving environment!! Onshore, the requirement for efficient transport, logging and testing was also met. This was a project which presented us with numerous new challenges, which our team overcame magnificently, and provided us with skills and experience we still use today on similar projects.

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