ROCK REINFORCEMENT
Epiroc has successfully introduced an
integrated pumpable two-component resin
system that can be used with a Self-Drilling
Anchor (SDA) style bolt in tougher ground
conditions
Technology advances in
bolting, meshing and
shotcreting are helping
to meet new operational
challenges in ever
deeper mines, reports
Paul Moore
Relieving the tension
s underground mining operations get
ever deeper in the search for ore, rock
reinforcement has become increasingly
difficult and more challenging. After several
years of research and development, Epiroc says
there is now a solution on the horizon. “The
major bottleneck for most underground mining
operations is the installation of rock
reinforcement in newly blasted areas.
Traditionally, rock bolt installation is done with
mechanised drill rigs drilling bolt holes before
injecting a bonding agent, such as cement
grout, and then pushing the bolt into the hole.
Rock bolt installation is often done in
conjunction with the installation of wire mesh,
which is used to help prevent smaller rocks from
falling from the tunnel surface. With higher rock
stresses, it is not uncommon for bolt holes to
become blocked with small pieces of fractured
rock, making installation of bolts difficult.”
LKAB, the major iron ore mining company in
northern Sweden with underground operations
at Kiruna and Malmberget, and a key
Sustainable Intelligent Mining Systems (SIMS)
project partner, has an existing rock bolt system
where it can take up to eight hours or more after
installation before the load bearing capacity of
the bolts is sufficient to allow operators to re-
enter the area to continue with the mining
process. In some areas, the rock conditions
make it nearly impossible to perform rock
bolting in a reliable fashion. “The bolting
process has been our major bottleneck for
years, and it’s the same wherever you look
globally. We’re good at sticking firmly to the
same old methods in this business,” says
Anders Johnsson, Project Manager at LKAB.
To address this rock reinforcement bottleneck
issue, LKAB joined forces with Epiroc in a
A
20 International Mining | AUGUST 2019
cooperative project in 2014, with the explicit
objective of increasing the speed of the rock
bolting cycle. The initial goal was to make the
rock bolting process twice as fast as systems
currently in use.
The project team started with a blank slate,
with several brainstorming sessions to explore a
wide scope of ideas and technologies. These
ideas were then whittled down to the most
promising paths forward within a reasonable
time frame.
Resin cartridges are a substitute for cement
grout with rebar rock bolts and are already
available and in wide use in underground
mining today. While resin cartridges offer fast
The integrated pumpable resin system from
Epiroc is designed to be used on the
mechanised bolting machines Boltec M and
Boltec E models, though an autonomous
version is in development
setting times, shooting the resin cartridges into
partially. Blocked bolt holes can prove difficult.
Similarly, when installing resin cartridge rebar
bolts together with mesh, there can also be
problems when you try to push the resin
cartridge shooter hose through the mesh wire.
Volume changes in the bolt hole due to any
cracks and voids in the rock can pose an issue
for resin cartridges, as the fixed volume of the
cartridges cannot accommodate volume
increases in the hole. The ultimate solution was
one with that provided short setting time for
resin cartridges, was indifferent to hole
blockages, and could be adjusted to work with
volume changes in the bolt hole.
“One of the most exciting technologies that
was looked at during the brainstorming
sessions was a pumpable form of resin. The
resin would fulfil the short setting time
requirements and being pumpable would also
address the issues related to volume changes in
the bolt hole. What was needed was a bolt type
that would allow the resin to be pumped
through it and enable reliable installation
regardless of ground conditions. Fortunately, a
bolt of this type already existed – the Self
Drilling Anchor (SDA), a rock bolting system
used for soil nailing, spiling and other
applications for reinforcement of bad ground
rock. The SDA bolt is a hollow tube with a
sacrificial drill bit at the end. It acts like a drill
steel during drilling and remains in the hole and
acts like a rock bolt once installed.”
“It was quite tricky to find the perfect balance
between the size of the bit and the drilling
capacity. We wanted it as small as possible, but
knew it needed to be able to drill three metres
or more. At the same time, the bolt itself needed
to be dimensioned to carry the injected resin all
the way to the end,” says Johnsson.
After some concentrated R&D work, the
resulting bolting process with SDA bolts and
pumpable resin became relatively straight
forward. The SDA bolt is drilled into the rock
mass and held in place. The bolt is then used as
the filling conduit to pump the resin through the
bolt and fills the bolt hole from the top down.
Using an innovative flushing technique, the
resin injection mixer is cleaned, with no
unmixed resin product being released. The SDA
bolt is held while the resin hardens in the hole
and is then released with the bolt fully installed
in the rock.
As part of proving the pumpable resin and
SDA concept, a modified Epiroc Boltec EC rock
bolting drill rig was used for a four-month field