Norwegian contractor, AS Birkeland Entreprenørforretnining, was nearing breakthrough as T&TI went to press on a 670m long tunnel that will tap a mountaintop lake to supply water to the Kløvtveit hydropower project in Norway.
The works are part of the first phase of the 41.8GWh Kløvtveit project for client BKK. Birkeland is carrying out the works in JV with Spilde, with Birkeland being mainly responsible for the underground scope and Spilde the surface works. The power station has already been completed, as has most of the penstock pipeline.
Birkeland is currently driving the last 85m of the 17% grade tunnel. As it approaches the lake, systematic probe drilling and grouting is carried out to prevent ground instability and a premature inrush.
With its Atlas Copco Rocket Boomer L2C30 rig, Birkeland became the first Norwegian contractor to order a rig with the company’s COP3038 highspeed drill. Håkon Birkeland, project leader and a director of the contractor said: “Drilling is definitely improved with the 3038. We had the COP1238 drill before, but these drills make an enormous difference.” The 4.3m wide by 5.1m high tunnel has been driven through hard gneiss. The crews have managed advance rates of 30m-55m per week using 59 blastholes in 6m long rounds. The chargeholes are 48mm diameter, with four 102mm reamed relief holes in the cut. The explosive used is ANFO initiated by Nonel LP detonators. T&TI was told average round pulls are only 5m. Ground support is used as required in poor sections. No permanent support is specified as the tunnel will be filled with concrete around a 1m diameter pipeline on completion.
Birkeland has also won the contract for phase two of the scheme, which will supply more water to the power station by way of three similar tunnels. These are due to get underway next year, with the whole project due for completion in 2007.
