Rocket Boomer WL3 C at Skatestraum's main face.

Why the sound of tunnelling is music to a veteran's ears

Veteran tunneller Jostein Fjosne enjoys the challenge of battling with the elements at remote sites, so long as his equipment doesn't let him down.

Mr Fjosne's current challenge is on National Route Rv 616, which will connect the mainland to the island of Bremanger in the Nordfjord on the west coast of Norway. The 4.9 km two-lane road will use the island of Rugsund, where it passes through a small tunnel, as a stepping stone to Bremanger.

Jostein Fjosne: "ABC Total has been a very positive development for us."

At the east end of Rugsund the proposed 470 m-long Krakevik tunnel will connect with a 311 m-long bridge to Kolset on the mainland. The road and tunnels on Rugsund will cost USD 8.5 million and the bridge around USD 5 million.

Meanwhile, Project Manager Fjosne is in charge of driving the 1.89 km-long Skatestraum underwater tunnel to complete the fixed link to the mainland. It is under construction from Bremanger to the west end of Rugsund, and will be the first underwater fjord crossing in the County of Sogn og Fjordane.

The tunnel will dive beneath the fjord with gradients of up to 1 in 10 to a point some 40 m below the seabed and 80 m below sea level.

ANFO charger for Dyno site mixed blasting agent.

Emergency measures

The Skatestraum link is being constructed to a standard which provides a 54 sq m finished section for two lanes of two-way traffic, and will be well-equipped with emergency stop zones with firefighting equipment and telephones.

It will be possible to use cellular phones and listen to the radio while driving through. In the event of an accident, police, fire brigade and ambulance will use dedicated radio channels.
The tunnel will be monitored at all times by the Emergency Surveillance Station in Floro, and by the Roads Administration controlling stations in Laerdal and Bergen. Extraction fans will start automatically to ensure good air quality at all times.

When completed, the new fixed link will offer ferry-free access to the mainland for the 1,900 inhabitants of Bremanger, with safe and reliable road transport for the products of its fishing industry.

Experienced rig operator Jan Berge: "The WL3 rig is the best on the market."

Rigs with a pedigree

The first 180 m of the Skatestraum tunnel was driven by a Rocket Boomer 353, previously used by Statens Vegvesen at the Aurland end of Laerdal, the world's longest road tunnel at 24.5 km.

However, since last January the tunnel has been driven using a state-of-the-art Atlas Copco Rocket Boomer WL3 C with ABC Total automatic boom control and Bever system profiling.
The rock conditions are gneiss, phyllite, and serpentite, with a zone of banded gneiss with quartz. The most important job for the WL3 C, which is generally in automatic mode, is to drill the six 27m-long probeholes that are maintained ahead of the face. These have to be drilled every 20 metres on advance to ensure a minimum overlap of 7 metres and threaded extension rods and button bits are employed for this operation.

The standard round comprises 92x45 mm blastholes with 4 x 102 mm cut- holes, all drilled to 5.2 metre depth for a 5 metre advance. The Rocket Boomer drills the entire face in under two hours, generally in automatic mode.

Transporting explosives at the Skatestraum portal.

ABC of drilling

The Skatestraum WL3 C features ABC Total, which is the most advanced form of boom control in the Atlas Copco ABC series. The drill pattern and the drilling sequence for each boom are created on the office PC using TML software, and transferred to a PC card.

At the face, the drill rig is centred and lifted on its jacks, and its position is confirmed by placing one of the feeds in line with the tunnel laser. The feed is adjusted so that the laser passes through the hole in the centre of its rear target plate and hits the centre of its front target plate.
The PC card is inserted into the rig computer, the drill pattern is read into it, and the booms automatically go to the initial start positions of their drilling sequences, and position and drill the programmed holes. If two booms risk collision, one will skip ahead to the next free hole. It completes the sequence and then returns to complete any missed holes.

Around twenty 2.4 m-long rockbolts are installed each round in roof holes drilled under manual control by the WL3 C drill rig. Two 9.5 h/day shifts are in operation, and two excavation cycles/day are being regularly achieved.

Comments Jostein Fjosne: "The WL3 is a big improvement on first-generation data rigs. Mechanically it is near perfect and, despite its size, it is easy to manoeuvre. ABC Total has been a very positive development for us, after some initial teething problems. The software is satisfactory and the rig is performing to its high specification.

"Our aim is to drill and blast the optimal profile at the lowest cost and the Bever Control system is serving us well with laser-accurate 3D scanning of the last round, providing documentation for the client as well as checks on the profile accuracy of the rig."