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  The Bjorøy tunnel – blasting on the seabed above the tunnel run ning through the “Bjorøyzone” (Jurassic sediments in the fracture zone)

  To improve navigational conditions in the fairway of Vatlestraumen, the Norwegian Coastal Administration was removing the underwater reef at Revskolten light. Revskolten reef is dredged to a depth of 14 metres, and it was removed 65.0000 cubic metres of rock from an area of 12.000 square metres. After construction work is completed, the new sailing width is increased to 250 metres. The construction work area was temporarily marked by buoys. During the work period, dredged mass was transported on a regular basis by barge to the land- fill area of Kleppesto, located approximately 5 nautical miles north of Vatlestraumen. Totally 65 000 tfm rock was removed on a 1200 m seabed and carried away by boat, to be used for widening a harbor 10 km away from the site. The total work was completed in 5 weeks’ time. Briefly said, the Bjorøy zone is about 10 to 15 m wide where open vertical cracks are filled with sand and silt down to the tunnel level, approximately 70 m below sea level. The main zone of sand and silt has a thickness of about 2 m, but with fragments of rock of Jurassic Age.

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