With more mines moving underground to access higher grade ores under open pits, the issue of securing and protecting these underground complexes increases in difficulty.
With so much traffic passing over the mines operations have to ensure that the tunnels are effectively strengthened and prepared in the case of rockfall.
Sandvik has developed a new concept in ground reinforcement for underground hard rock mines that is reportedly faster and easier to install than traditional systems, while at the same time providing stronger ground support.
Dubbed the Sandvik Mechanical Dynamic (MD) Rockbolt, it replaces a range of different ground support systems such as resin bolts, stiff splitsets, and even cable bolting.
“The problem with resin bolting is that it’s not reliable due to the relatively large-diameter holes which have to be drilled in hard rock mines,” Sandvik Mining’s manager for rock reinforcement development Mietek Rataj.
“This is because the resin is frequently poorly mixed so the bolts are not anchored properly in the rock.
“In addition, their installation can be very slow, and they are relatively rigid two-pass bolts, so they are not suitable for dynamic ground conditions,” said Rataj.
“In contrast, the MD Rockbolt is a dynamic bolt which is able to yield and withstand changing ground conditions, it’s a one-pass system, with no need for any grouting,” he said.
MD Rockbolts are galvanised, come in 2.4 m and 3 m lengths, and are rated to hold up to 30 tonnes.
The system is particularly suitable for moving ground conditions as it slides at high load, maintaining high capacity support.
Peter Young, Sandvik’s product line manager for the Rockbolt MD said that “similar to a standard friction bolt, the MD bolt is installed in a single pass, with a simple twist to anchor it once it’s in the ground.
“There’s no chemical insertion or grout injection required, and no need to come back later to tension up the rebar.
“We’ve had feedback from one mine that they had an area of ground where they struggled to install just a few resin bolts because the ground was so poor; over that same period of time, they had successfully installed 100 MD Rockbolts.”
He went on to state that “they are a direct replacement for resin bolts, so anywhere you can put in these bolts, you can use MD Rockbolts – plus you can put them into very challenging or difficult situations where other bolts just don’t work.
“They may even replace cable bolting to a degree. There is one application in Australia where the mine was able to delay the installation of their cable bolts from 25 metres of driveage out to 50 metres,” said Young
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