The old wreck lies on the seabed, split in two main parts with smaller debris scattered across the wreck site. The bow, which is resting on a slope on the seabed, is the most exposed part and geotechnical calculations have shown that this slope is very unstable. The aim of the project is to stabilize the seabed near the wreck in order to prevent the bow from sliding deeper into the ocean at a later stage. Experts from NGI are part of the large-scale subsea operation to secure the submarine and the mercury on the seabed floor.
The video shows the installation of the bow motion detection system attached to the hull of the submarine. (Video: Van Oord/NCA/NGI)
In January 2015, the Norwegian Ministry of Transport and Communications commissioned the NCA to prevent further contamination of the seabed and to construct a counter-fill to stabilize the unstable slope on the seabed.
Accompanied by the main contractor working on the project, the Dutch company Van Oord, NGI experts began working on the site, approximately two nautical miles offshore near the island of Fedje in Western Norway, in the beginning of May.
Smart solutions on the seabed
"We developed and built a specialised rig and used a ROV (Remotely Operated Vehicle) to install pressure probes at six different places on the seabed which will be covered by the counter-fill. The purpose of the probes is to measure the stabilization rate of the sediment during the filling process", says Stephen Hayes, Senior Specialist with NGI's Section for Instrumentation and Monitoring.
The illustration shows the position of the bow, resting of the unstable slope on the seabed. (Courtesy: Norwegian Coastal Administration)
In order to detect even the slightest movement of the submarine's hull while constructing the counter-fill, NGI also built customised motion sensors capable of detecting vibrations and any slight changes in the inclination of the hull. The measurement devices are connected to the national system for environmental monitoring, provided by the NIVA (The Norwegian Institute for Water Research) and they continuously transmit data to a dedicated surveillance vessel near the site.
The Norwegian Coastal Administration describes this monitoring programme as being the most comprehensive programme ever to have been conducted for an underwater operation in Norway.
This animation shows the enormous project on the seabed off the coast of Norway. (Courtesy: Norwegian Coastal Administration)
- The British submarine HMS Venturer torpedoed the German U-864 submarine on 9 February 1945. The German submarine had a crew of 73 and a cargo of approx. 65 tonnes of mercury. Both subs were submerged when the incident occurred.
- The Royal Norwegian Navy found the wreck of U-864 in 2003, two nautical miles west of the island of Fedje in Norway. The wreck was split into two main parts, with the bow lying on an unstable seabed.
- Approximately 100,000 tonnes of sand and rock goes into constructing the counter-fill, which will be able to withstand major disturbances such as earthquakes on the seabed.
- The counter-fill will stand seven metres tall and is due to be completed before the summer of 2016.
- In addition to the main contractors Van Oord and the NGI, other partners working on the project include DNV GL, Geopartner Marin, Kvale, NIVA, Reinertsen and Rambøll.
- Visit the Norwegian Coastal Administration's Facebook page on U-864: https://www.facebook.com/u864fedje/