Twin tunnels

Norway-Based Mika Is Currently driving two single-track tunnels through Gammherrgård Mountain in Husum, about 85 km southwest of Umeå as part of Sweden's new SEK 13,2 billion (€ 1,4 billion) Bothnia Line railway.

The 227 and 233 m tunnels, both with a cross-section of 68,5 m², are being driven using a Tamrock Axera T11 Data drill jumbo, a computer-controlled 3-boom rig. For drifting, the rig is using 6 m Sandvik Extra T35-R35 MF drifter rods and 48 mm drill bits.

The same rods are used for extension drilling after every third round, using 54-mm bits to drill 22 m holes to install a grout shield over the tunnel area. Rock bolting, too, is carried out using the same rig and rods. The computerised drilling system uses a drilling pattern consisting of 137 holes. High demands on the tunnel contour calls for smooth blasting, which requires many, closely spaced perimeter holes to be drilled.

According to MIKA drill rig operator Johan Magne Hansen, “Computerised drill rigs have improved the working environment. We no longer have to mark out the drill holes on the face, the rig positions the booms and drills the holes automatically and the operator has a comfortable workstation.”