Spotlight Feature Articles Ansul Modern Open Pits February 16 | Page 3
MODERN OPEN PITS_proof 21/10/2015 10:05 Page 2
MODERN OPEN PITS
mining operations were to be conducted in close
proximity to the walls.
In November of 2014, the ring net mesh
system was successfully installed and operations
resumed. This plan makes it possible to mine
the remaining 175 ft of ore safely, below a 2,000
ft tall highwall. The project was completed
safely and with no incidents.
Mastering rockfall protection
IM also spoke with Roland Bucher, General Manager
of Geobrugg Australia Pty Ltd. Swiss parent
company Geobrugg is well known as a global
leader in the supply of high-tensile steel wire
mesh; while its rockfall protection systems provide
effective protection for people, infrastructure,
equipment, access roads, tunnel portals, and
buildings. Its slope stabilisation systems
provide highly sustainable solutions for securing
unstable slopes or for reinforcing existing retaining
structures of any kind as well as shotcrete walls.
On demand for these types of solutions at
minesites, he states: “It is not a straightforward
answer, it all depends on the individual pit,
especially the geology, and both the strategic
and safety approach of each mining company.
The orientation and steepness (dip) of the
orebody and therefore the rock mass in the pit
slopes – both the footwall and hanging wall – in
terms of structures and orientation, as well as
possible blast damage on the pit slope, are
factors to consider.”
In terms of the differences between the
approach to rockfall protection and slope
stabilisation installations between mining and a
road cutting for example, “mining projects tend
to be considered temporary, with a requirement
for a shorter design life, but with the likelihood
of higher rockfall frequency. Along a road or a
railway corridor the likelihood of a rockfall or an
impact is generally lower but the exposure is
much longer, such as a design life of 50-100
years.”
Some Geobrugg mining applications are
customised designs to fit the site’s specific
requirements. Most of the time, standard
systems, which are 1:1 field tested can be used.
On the use of radar monitoring in conjunction
with its technology, Bucher states: “Radar is
used as a monitoring system, whereas what
Geobrugg offers are mitigation systems. These
are often used side by side, or one is chosen
over the other based on the specific issue and
strategy on site.”
Companies like Geobrugg are often contacted
after a rockfall event has happened, to keep a
certain work area in the pit safe from rockfalls
and to continue with the mining process in that
area thereafter. In recent times, some of the
mining companies have been reviewing their
slope design/angle and try to steepen certain
pit slopes to either access more ore or reduce
the waste movement (improve the strip ratio).
Mitigation systems like rockfall barriers (catch
zone one
zone two
Safe, flexible survey
and monitoring solution
Proactively manage geotechnical risk and help
maintain site safety with Maptek Sentry.
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•
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Survey and monitor with a single system
Track surface movements and analyse trends
Map highwall structures from detailed 3D laser scan imagery
Use rockfall data to maintain geotechnical databases
Act quickly and decisively on safety measures
[email protected] | www.maptek.com
fences), mesh drapes or slope stabilisation are
considered in certain areas to achieve the
steeper pit slope design and maintain the same
risk level.
An example of recent project work is at
Grange Resources (see Hutchison B.J.,
Macqueen G.K., Dolting S.L., Morrison A-T. 2013.
Drape mesh protection at Savage River Mine,
Tasmania. Slope Stability 2013, Brisbane,
Australia, pp 1,345-1,359), which in 2010
experienced two large wall failures at their
Savage River mine in Tasmania, Australia. These
rockslides buried a significant portion of the
magnetite ore scheduled to be mined in the
following two years. To ensure long term ore
supply, a major cutback was required to get
back down onto the orebody. Several different
approaches and mine plans were considered
before deciding on a cast blast and drape mesh
option to speed up the bench advance. Various
mesh design schemes were assessed, before
selecting a Geobrugg drape mesh system to
cover the 60 to 80 m high, steeply dipping,
haematite coated shear. The intent was to allow
rapid mining bench advances during the cutback
and rockslide removal process. By adopting this
approach considerable time was saved by
eliminating extensive pre-splitting, trim blast
and rock support requirements associated with
Grange’s normal mining procedures.
Two large cast blasts were taken to remove
rock material in front of the back scarp. The cast