From March 2016 until August 2017, Strukton Immersion Projects (SImP), a company part of Strukton International, worked on the immersion of five gravity based foundations (GBFs). The location for this offshore wind power project is 6 km off the coast of Blyth, near Newcastle (UK).

The project was owned by EDF Energies Nouvelles Group and operated by EDF Energy Renewables. SImP, as subcontractor of BAM JV, was responsible for the marine scope, the float and submerge of five GBFs, including the sand ballasting and installation of the GBFs. Each GBF weighs more than 22,000 tonnes when fully installed. They were immersed at a water depth of 40-45 meters.

The float out and transport of the GBFs was started in July 2017. The five GBF elements were moored at a mooring location were the final works were performed before transport over the river Tyne. The GBFs were then brought to their final destination where the immersion with water was completed. After this process, the GBF’s were ballasted with sand to make sure they are stable to receive the top parts of the windmill.

For this last step, SImP constructed a pontoon of 100 by 30 meters, containing a sand storage (8000 m3) and two pump systems consisting of pumps and a mixing unit to mix sand with water. The pontoon is custom-made and exclusively used for this project. The technique developed by SImP to use sand for the purpose of immerging the GBFs, is innovative and unique. In general, a wind mill has a life span of approximately 25 years. By using sand instead of concrete, the GBFs can be dismantled by removing the sand, after which the structures can be recycled.

On August 31 2017 the sand ballasting of the last GBF was completed. The wind turbines are installed on top of all five GBFs. The wind mills will now produce low-carbon electricity for 34,000 UK households. They will save 57,600 tonnes of CO2 emissions each year.

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