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MODERN OPEN PITS
Geobrugg TECCO G80/4 mesh anchor system
layout and crest mesh at Grange Resources
Savage River in Tasmania

Pushing back boundaries
Paul Moore reviews some industry advancements that
benefit open pit miners, from rockfall hazard protection, to
slope stability monitoring with radar, but also better
identifying gaps in availability
n a paper entitled, Proactive controls for
highwall stability, Trevor Ames, Mining
Geotechnical Services Director at geohazard
mitigation group GeoStabilisation International
(GSI) states: “Periodic examination of highwalls
and limiting access to potential hazardous areas
are measures that should be incorporated at all
open pit operations with best practices for
proper equipment handling techniques near
highwalls and operator training in the
recognition of highwall hazards. Incorporating
engineered controls should be a proactive part
of every operation’s ground control plan to
reduce the likelihood of highwall instability and
rockfall hazards. A continuous assessment into
geotechnical design modification must be
undertaken to continually improve the integrity
of the final highwall design. Sound blasting
practices to minimise the negative impacts of
overbreak and excessive vibration can aid in
maintaining the design integrity throughout the
mine life. Additionally, to combat ravelling and
further induced ground movement, an effective
scaling maintenance program and rock
reinforcement should be evaluated to provide an
economically viable solution to safeguard the
operation against geohazard events.”
He then summarises the several methods that
exist to reduce the hazards related to ground
instabilities from a highwall, including scaling,
provision of adequate catchment area, and
ground reinforcement. Scaling is an operation
where rocks on the highwall are checked for
stability with a miner’s bar. If loose blocks are
encountered, they can be removed from the
highwall under a controlled environment.
Mechanical and hand scaling are two
predominant approaches to scaling slopes.
Mechanical scaling is a more economical
approach because large areas can be scaled out
at a much lower cost. The inherent danger in
mechanical scaling is that equipment can
undercut structures that were secure enough to
apply a different stability approach and avoid

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42 International Mining | NOVEMBER 2015

inducing wider stability issues. Hand scaling is a
more common approach to initially remove any
unstable rocks.
“A second common approach to dealing with
rockfall hazards is to provide an adequate
catchment area at the base of the highwall. An
experienced geotechnical engineer or geologist
can assist in providing requirements of an
adequate catchment area with tools such as the
Catchment Area Design Guide. When measures
are needed to handle rockfall hazards beyond
scaling and providing there is an adequate
catchment area, many other remediation tools
are available. These include the use of dowels,
tensioned anchors, draped mesh, pinned mesh,
rockfall fences, hybrid systems, and berms.
Selecting a ground reinforcement method relies
heavily on a good working knowledge of the
local ground conditions in determining the most
effective design.”
There are several variations in mesh designs
providing different load capacities. Their
application includes areas of highly weathered
rock near high traffic areas such as access
ramps and portals. This provides an adequate
measure to reduce the risk to mine personnel
and infrastructure by controlling rocks as they
fall from a highwall. “Control of the rockfall
reduces its energy and contains the rocks to a
catchment area where they can be collected and
removed in a safe manner; minimal maintenance
is required if designed properly. The type of
material used for the mesh design should be
scrutinised to make sure that it can manage
potential rockfalls without tearing and creating
gaps in the system.”
Flexible rockfall barriers, also called rockfall
fences, contain falling rocks from moving into
protected areas. Th W6R7