Installation of the GBF®
1. The foundations will be produced at an industrial scale using a production line technique.
2. A dedicated heavy lifting steel frame will lift the tower elements and the nacelle on top of the concrete bases. Then the hub and blades will be mounted. Finally, the turbine and its foundation will be lowered into the water, ready for pick-up.
3. The GBF® will use a purpose-built unmanned transport installation barge (TIB). For the pick-up, the TIB will be ballasted down to the level of the base then, upon connection, will refloat to transportation depth.
4. The TIB will then be towed to the wind farm site, where it will be ballasted to lower the wind turbine into position in the prepared seabed. The TIB will then release the gravity base, move away, and be re-floated, ready for its return journey.
With a maximum of work performed on shore and with installation by unmanned barge, this foundation concept leads to improved safety and quality concrete. Looking into it makes perfect sense. GBF® project manager Kevin Bennett explains the concept.
By Anne Korsgaard
Floating cranes and jack-up barges are unnecessary for installing gravity base foundations; you can use a comparatively inexpensive purposebuilt transport and installation barge (TIB). This is one of the big money savers, according to Kevin Bennet. Suited for water 30 to 45 meters deep, the GBF® is a competitor for the Round 3 in UK waters. Optimizing use of materials, production lines, and installation barges, this joint venture between three specialized companies shows that there is strength in cooperation.
Material costs represent a great advantage inasmuch as reinforced concrete is not subject to large fluctuations in price, and the materials will provide local employment at wind farm sites.
The foundations and turbines are mounted onshore then transported to sea and released onto the seabed.
GBF® is a joint venture between three companies, which was initiated through the Carbon Trust foundations competition (read more in the article on pages 6-9). Gifford brings extensive experience in the design of marine structures; BMT’s expertise is in the naval architecture of the transport and installation barge (TIB); and Freyssinet contributes specialist construction knowledge, especially in the handling of heavy objects.
When asked about the major challenges for the gravity base foundation, Kevin Bennett explains:
- The greatest challenge seems to be persuading the industry that the cost, safety, and quality advantages of installing so many components onshore rather than offshore deserves a rethinking of the traditional procurement process. Moreover, we need to convince some actors in the sector that we can deploy the gravity bases efficiently and accurately with the TIB.
Another challenge lies in the installation process. According to the GBF® project manager, the slipforming of the gravity base is a straightforward operation:
- The challenge, however, is to do this in an industrial process so that efficiencies are maximized and costs are brought down.
And in terms of hopes for the future regarding the gravity base foundation, he points out:
- Hopefully, we will be invited to further de-risking in Carbon Trust, possibly through tank testing of scale models. The objective would be to verify that seakeeping, ballasting, and release mechanism designs are all satisfactory.
Learn more at www.gbf.eu.com