Mercury Filled U-Boat wreck stabilisation

20th September 2017.

Per Magnus Sparrevik’s will speak on securing 67 tonnes on mercury on an unstable sea bed.

Historical background, environmental and geotechnical conditions are presented for the challenging remediation work performed so far by the Norwegian Coastal Administration in order to protect the marine environment from the toxic legacy of U-864, a German submarine sunk by the British navy outside the west coast of Norway near the end of the Second World War. As the sloping seabed at the wreck site is unstable, the first step was to install a large counter fill to prevent sliding of the heavily contaminated sediments.

The large counter fill was successfully installed in June 2016 at the foot of the unstable slope where the wreck is resting. A rigorous monitoring program of both environmental and geotechnical parameters indicated that no further spreading of contaminated sediments occurred during the construction of the counter fill. Initial piezometer readings show that the build-up of excess pore pressures beneath the counter fill during construction match the predictions very well. The ongoing autonomous recordings of pore pressure and settlement data are vital to verify the rate of consolidation and determine when the slope is sufficient stable to allow for further counter filling and final capping of the wreck and contaminated sediments.