Norway has a lot of tunnels. Over 4,700 kilometres, in fact. It’s not that the 4.6 million inhabitants have a particular affinity for making life hard for themselves, but rather because Norway is a rocky, rugged, mountainous land where it’s simply easier to dig through rather than climb over.
Norway’s infrastructure has struggled to keep up with the demands of its busy population, especially around its capital, Oslo, where up to a quarter of the population live. As part of an ambitious plan to upgrade the national rail network, a 20 kilometres (12.4miles) long double line railway is being built from Lysaker to Sandvika – from the west of Oslo into its centre. The new line will make extensive use of tunnels and dramatically increase transit speeds and capacity for both passenger and freight rail traffic. The key part of the project is a 5 kilometres (3.1miles) tunnel, of which global contractor NCC is building 1.8 kilometres (1.1miles) of it.
With all its experience, Norway has become the centre of excellence in drill-and-blast tunnelling techniques through hard rock. The stability of its solid, very old, largely Gneiss rock which is up to 3.5 billion years old.
NCC’s construction manager Simen Thorsen, himself an experienced tunneller, modestly describes the project as ‘relatively straightforward’.
“What complicates matters is the geometry of the installations,” he says.
“Cutting the niches for the rail infrastructure, and creating a tunnel profile that allows train drivers a clear line of sight to rail signals needs careful attention. Because of this we are using the latest technology to make sure we get it right.”
The tunnel is being constructed using a combination of drilling and blasting, and an advanced Norwegian-built jumbo drill, at the sharp end of the project, is being assisted by an exclusively Volvo team of construction equipment.
The team is making up to 45m (147ft) of progress per week, each blast gains 5m. Drilling of up to 200m (656ft) an hour is taking place, and every third blast a process of injecting cement grout is conducted to provide waterproofing support and preserve the water table. This is not the only environmental measure: noise, dust and vibrations are all closely measured. All water on site is recycled and purified, so that it is almost as clean as drinking water.
The key support to the project is a Volvo L350F wheel loader. Its role is to load the project’s three Volvo A40E articulated haulers with blasted rock. The haulers are a perfect match for the wheel loader – whose capacity equates to four passes of the wheel loader's bucket. Central to the operation and with no back-up machine in support, the loader simply can’t break down. Since arriving on site in February 2008, it simply hasn’t. The site also has Norway’s first EW210C wheeled excavator, fitted with a special tilting cab and rock scaler attachment, which removes any loose rock left by the blasts.
Other Volvo machines on the project are a Volvo L90E wheel loader that is doing fetch and carry duties and a pair of backhoe loaders with trailer fitted for carrying drainage pipes. The project’s ‘mascot’ is a 1970s vintage Volvo BM 4300 wheel loader with over 30,000 hours on the clock – and still working hard.
Because much of the site runs through an urban area, there are also time limits on when rock can be moved out of the site. This could create a backlog of blasted rock at the tunnel face, which would cause delay. To overcome this NCC, a specially built subterranean ‘reloading station’ allows the high capacity removal of spoil from the tunnel face. The loaded haulers take blasted rock and dump their loads down a shaft into a manmade chasm 25m (82ft) below sea level. Here a Volvo L180 E wheel loader loads a team of on-highway tipper trucks that gain access via a specially built tunnel.
“In one week it loaded 12,186m3 (430,000 ft3) of blasted material – so we’ve kept it busy,” says Simen.
The rocks are then dumped in nearby Drammen for reuse as rock amour for a new harbour that is
being built.
“The drill and blast process means that there is plenty of time for maintaining our machines properly,” continues Simen.
“This is important as if any machine breaks down the whole process falls apart. But if you treat machines well they should not stop. On this job we have made such good progress that we are well ahead of schedule and have exceeded the theoretical maximum advance for several weeks in a row. You always need a bit of luck with tunnelling – but that’s exceptional progress.”
Read more at www.volvogroup.com/movingtheworld