Concrete results down the road
For nearly 80 years Boliden has mined ore in the Kristineberg mine – and the challenges have grown as the working depth has increased. Geological conditions mean that half the time is spent reinforcing rock, rather than mining it. Together with Atlas Copco, Boliden has started on a journey to tighten up the bolting process.
Sunniva Haugen, Mine Manager, Boliden
The headlights of the Boltec LC rock bolting rig light up the walls and roof of the concrete-covered drift. The last dark patches have almost completely disappeared. “The concrete’s now been hardening long enough for me to be able to start bolting,” says operator Magnus Linder, fixing his gaze on the screen in the cabin of the bolting rig.
He focuses the optical instruments on the last row of bolts in the wall of the drift, “zeros” the rig on them and enters the preset bolt pattern in the Bolt View program. The screen shows him exactly where to position the bolts to form a perfect fan, with a gap of 1.2 meters both between the bolts in the rows and between each row. Magnus directs the boom towards the wall and drills with the drill steel, then changing over to the cement hose and filling the hole with cement. Finally, he uses the rig’s bolt driver to drive home the 2.7 meter long rock bolt – a reinforcing bar with a threaded end and a plate at the far end. Another 59 bolts and the drift will have been sufficiently reinforced.
Boliden has been mining ore in the Kristineberg mine, situated in Lycksele municipality in northern Sweden, since 1940. Initially a large part of the production was from open-pit mines, but now all the ore is mined underground – right down to a depth of 1 350 meters. The high rock pressure and the weak nature of the rock mean that the rock has to be reinforced so that it does not collapse after blasting. Walls and roof are coated in sprayed concrete, and the drifts are then reinforced with long bolts.
“Half of the drill-and-blast cycle time is spent on reinforcing the rock,” says Mine Manager Sunniva Haugen. “That’s a huge amount of time. Rock reinforcement is vital for safety, but generates no revenue. Bolting takes twice as long as blast hole drilling and is the bottleneck in the mine – in other words, the limiting factor on production capacity. The more bolts we can get in, the more rock we can mine.”
In 2016, Boliden began working in partnership with Atlas Copco and ABB to streamline the bolting at Kristineberg. The Boltec Optimization (BoltOpt) project aims to reduce the time it takes to drive drifts by 20 percent. The work began by collecting a large amount of data, primarily through Atlas Copco’s telematics solution Certiq (that gathers, compares and communicates vital equipment information) and Boliden’s own systems, but also from field studies and by talking to operators, technicians and supervisors. Having compared this information with performance indicators, Atlas Copco – in dialog with the operators – came up with suggested improvements. The main conclusion was that the logistics down in the mine could be tightened up.
“The aim was to find time thieves, and we got them in black-and-white thanks to Atlas Copco,” says Michael Andersson, Development Engineer at Boliden’s central technical department. “We were aware that a lot of time was being lost both through transporting people and replenishing stocks, but we didn’t realize how much.”
Epiroc operated under the name "Atlas Copco" until January 1, 2018.