In the summer of 2013, the Printzsköld orebody in LKABs iron ore mine in Malmberget, Sweden, was closed due to high seismic activity in the mine’s production levels, between 920 and 996 meters depth.
The area contained high levels of soft biotite that made it subject to squeezing of the rock mass and subsequent risk of rock fall. Consequently, LKAB management decided to temporarily close the affected areas and suffered significant production losses.
To enable reopening of the mine and further production in the closed section, a project to rehabilitate the 3400 meters of affected stope was approved. The project represented an investment of approximately 50 million SEK (M€ 5.3) in a comprehensive system of dynamic rock support, including sprayed concrete, dynamic bolts and mesh.
Normet’s D-Bolt® was a vital part of this project, which with the reopening of the mine in November 2013 – two months before the project plan, was deemed a great success. In combination with previously applied steel fiber sprayed concrete and mesh of 70 mm rebar squares, the 3 meter long Ø20 D-Bolt® installed in patterns of 1 x 1 meter, make up LKAB’s highest level of dynamic rock support. 40,000 D-Bolt® were installed as part of the rehabilitation. “This is our highest safety class and is required for the rock conditions that are present at Printzsköld”, says Kjell Harnesk, rock mechanics manager at the LKAB Malmberget mine. He says the project is important for the future of ground support at Malmberget: “The Rock reinforcement work has given us useful experience. From now on we will work to install dynamic support as a natural part of the production cycle”, says Harnesk.
Rock mechanic Stefan Lindahl was LKAB’s project leader in the rehabilitation, and he is very satisfied with the installation process and progress of the project which employed seven bolt and mesh rigs working 24/7.
“We were able to work without disturbances and finished two months before plan”, Lindahl says of the work that was mainly carried out by the contractor Bergteamet.
Bergteamet’s site manager, Mats Ragnarsson, contributes part of the installation success to the D-Bolt’s ease of use: “D-Bolt® is installed in the same way as the rebar bolts, but is easier to handle than these. D-Bolt® is a little more expensive than the rebar bolts, but the difference is outweighed by the increased safety.”