A consortium of Nordic contractor, NCC, and local companies has been commissioned to construct the US$41.3M, 6.2km long Nordoyatunnilin road tunnel linking the most northerly Faeroe Islands of Eysturoy and Bordoy. Excavation of the 420,000m3 of rock is scheduled to start immediately on what is said to be the Island’s second longest sub-sea tunnel.
The 64m2 cross section area tunnel will be constructed by drill and blast from two faces, one from each portal, mainly through basalt. At each face, advance rates of up to 45m-50m per week are expected through the basic volcanic formation that is considered good quality for tunnelling and requires minimal support.
The Q-system was used to assess the rock mass classification and support design but, as the system is not considered completely suitable for basalt, it will be used purely as a guide. Actual support will be based on specific geological conditions in the immediate vicinity and is expected to include minimal rockbolting and a 600mm thick shotcrete lining.
During excavation, probe drilling ahead of the faces will be used to detect weak rock and possible water bearing zones.
As the maximum water leakage allowed into the tunnel is 300l/min/km, a pre-grouting mass has been calculated to be 170km/m of tunnel consisting of rapid cement.
Finally, the 70,000m2 tunnel surface will be waterproofed with mats of fireproof PE lining, ready for the scheduled completion date in August 2006.
NCC’s portion of the contract is valued at US$35.3M. The contractor has already experienced tunnelling in the Faeroe Islands having completed the island’s first sub-sea tunnel, the 4.9km long Vagar Tunnel, in January this year, six months ahead of schedule (June 03, p45).
