Yeoman Halsvik help stabilize WWII wreck
Aggregate Industries subsidiary protects Norwegian coastline with specialist material
AGGREGATE Industries’ subsidiary Yeoman Halsvik have successfully helped to stabilize the wreck of a World War II submarine, near the island of Fedje, on the west coast of Norway.
German submarine U-864 was sunk by the British in 1945 while transporting war load to Japan – including a large quantity of mercury. As a result of the torpedo attack, the submarine broke into sections that settled on the seabed at a depth of 145–160m.
The wreck was located in March 2003 by the Royal Norwegian Navy, at the top of a steep slope in the seabed, where it was discovered that the mercury had been seeping out of rusted containers and contaminating the region and marine life.
The Norwegian Government has since extensively assessed the best-possible solution to stabilize the wreck and contain the toxic mercury. It was recommended that ‘entombing’ the wreckage under a layer of sand and gravel would be the safest possible option.
At the end of 2015 the Norwegian Coastal Administration awarded the contract to Van Oord to carry out the works.
Subsequently, Van Oord enlisted the expertise of Yeoman Halsvik to provide a specialist material that would effectively perform the job of sealing off the seabed, preventing any future release of mercury.
Yeoman Halsvik supplied a specialized sand to comply with Van Oord’s requirement, as well as sub-base and offshore material from their quarry based at the Port of Slovag, on Norway’s west coast.
Van Oord implemented a thorough quality-control procedure to monitor the spreading of the materials and to ensure that there would be no risk of any potential seabed contamination during the installation process.
At a working depth of 150m, Van Oord built a foundation (counter fill) of more than 35,000 tonnes of specialist sand and 160,000 tonnes of stone, to guarantee the stability of the seabed slope and ensure that the surrounding sediments would not slide off.
Preventing the spread of mercury to the environment was the main objective during the installation of the counter fill, and stringent requirements were set for environmental monitoring of the work.
Van Oord also developed a special installation method for the placement of the sand, in order to minimize disturbance to the seabed.
As the exact volumes were not known and the installation time was relatively short, Yeoman Halsvik had to ensure sufficient production capacity and quick loading of the delivery vessels, which they successfully achieved.