Extension of the dry-dock at Haakonsvern has been a great challenge with blasting and heavy construction works within a sensitive defence area in full operation, environmental aspects and consideration to neighbours and 3 person, H&S related matters, stability of high rock walls with sequential excavation and support as well as logistics and transport of rock spoil within a limited area. Stability analyses are performed by using the programmes Dips, Swedge and Unwedge. The stability of the high walls of the open part, and walls and roof of the underground part of the dry-dock are found to be good by implementing the rock support measures as systematic rock bolts, shotcrete and rock anchors. Some of the identified potential slide mechanisms are sensitive for joint water pressure and drainage holes are bored as part of the support measures. Behaviour of the surrounding rock masses during excavation are monitored by measuring rock stresses and deformation. Results from the monitoring devices indicate that deformation and stability are under control. Clever planning and creative thinking as well as good cooperation and communication between the involved partners (Client, Contractor and Consultant) were required to secure safe performance, good progress and successful results during the construction and rock excavation works.


Altogether 5 new navy vessels, frigates in the "Fridtjof Nansen" class were produced and delivered in the period 2006 – 2009 to the Norwegian Navy. For maintenance and repair of the new vessels, extension of the existing underground dry dock was necessary. The Client was the Norwegian Defense Estates Agency (NDEA), design works was done by Sweco Norway AS and the main contractor was NCC Norway. Detailed design started in 2003, construction works in 2006 and completed in 2008. The first of the new vessels was ready for maintenance in the dry dock in June 2010.


The old dry dock at Haakonsvern was an underground rock cavern with approximately 150 m length, 40 m height and approximately 20m width. With a length of 135m and maximum width of 17m of the new vessels the rock cavern had to be extended both in height and width. The first 100m of the cavern had to be opened. A picture of one of the new vessels is presented in figure 1 and a longitudinal section of the old and new cavern with the vessel installed is presented in figure 2. Estimated key figures for the major rock works during design (rock excavation and support measures) are presented in table 1.


The dry dock at Haakonsvern naval base is located in massive granitic gneiss belonging to the Øygard rock formation...The formation is metamorphic rock of late precambrian age (800 – 1000 mill. years ago) which was deformed and metamorphosed during the Caledonian period (4 – 500 mill. years ago). The bedrock is massive without fault zones except from a minor fissure zone crossing the formation in NNE – SSW direction. From surface mapping, four different joint sets are identified.

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