Reopening a mine two months in advance with 40,000 D-Bolt® installed
The Printzsköld orebody in LKABs iron ore mine in Malmberget, Sweden, was closed in the summer of 2013 after high seismic activity in the mine’s production levels, in the depths of 920 to 996 metres.
The area contained high levels of soft biotite that made it subject to squeezing of the rock mass with subsequent risk of rock fall. LKAB management decided to temporarily close the affected areas and consequently suffered significant production losses.
A project to rehabilitate the 3400 meters of affected stope was approved to make the reopening of the mine and further production in the closed section possible. The project constituted an approx. 50 million SEK (M€ 5.3) investment in a comprehensive system of dynamic rock support, including sprayed concrete, dynamic bolts, and mesh.
- Rehabilitating 3400 meters of affected stope to reopen a mine
- 40,000 D-Bolt® installed
- D-Bolt® ease of installation and safety remarkable
- Reopening of the mine two months in advance
Normet’s D-Bolt® was a vital part of the project. In combination with previously applied steel fibre sprayed concrete and mesh of 70 mm rebar squares, the 3-meter long Ø20 D-Bolt® installed in patterns of 1 x 1 meter, consist of LKAB’s highest level of dynamic rock support.
“This is our highest safety class, required for the rock conditions that are present at Printzsköld. 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”, explains Kjell Harnesk, rock mechanics manager at the LKAB Malmberget mine of the project’s importance for the future of ground support at Malmberget.
The reopening of the mine in November 2013, two months before the project plan, was a success.
LKAB’s project leader in the rehabilitation, Rock Mechanic Stefan Lindahl was 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 remarks of the work that was mainly carried out by the contractor Bergteamet.
Bergteamet’s site manager Mats Ragnarsson agrees. “The 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” explains Ragnarsson, contributing part of the installation’s success to the D-Bolt® ease of use.