SLOPE STABILITY MONITORING
placed digitally on the wall in GroundProbe’s
patented SSR-Viewer software. At Filminera
Resources Corporation’s Masbate Gold Project,
an open-cut gold mine in the Philippines, the
loss of a significant number of physical prisms
due to vandalism had compromised the site’s
ability to detect and measure deformation,
thereby reducing the on-site geotechnical team’s
confidence to effectively manage risk. As a result,
the GMS-Dual was deployed to the site – which is
currently undergoing an active production stage
– to provide long-term, broad-area, background
monitoring.
“The GMS-Dual was selected due to its unique
prismless monitoring functionality whereby users
are able to detect deformation across the slope
by placing virtual points anywhere on the wall
within SSR-Viewer, our geotechnical monitoring
and analysis software,” says Fernanda Carrea,
Product Manager, GroundProbe. “The GMS-Dual
is then able to reflect its laser signal directly off
the rock, corresponding to the exact location and
placement of the virtual points in SSR-Viewer,
allowing it to detect hotspots of movement
across the area of interest.”
Virtual points can also be utilised when
monitoring areas that are difficult, dangerous or
even impossible to physically reach,
consequently inhibiting the installation of
physical prisms. In addition, as many virtual
points as needed can be placed in as many
locations as required, allowing the GMS-Dual to
detect deformation across vast areas and at long-
range. The GMS-Dual was easily deployed in just
minutes and positioned looking down to one of
the mine’s main pits, where hundreds of virtual
points were digitally placed on the slope.
“Within days of monitoring, the GMS-Dual
provided extensive practical data on the overall
stability of the pit,” said Prastowo Harymurty,
GroundProbe’s Technical Specialist who deployed
the system. “It also proved its competency in
detecting and tracking both positive and negative
deformation trends across each of the different
types of points; Prism Point, Pixel Point and
Precision Points. The GMS-Dual monitored
continuously and without interruption,
successfully detecting sub-millimetre movement,
reflecting its high accuracy and precision.”
The data gathered enabled the on-site
geotechnical team to identify areas with
differentiated geotechnical behaviours and
deformation trends; for example, some zones
featured no significant movement while others
either presented noticeable linear or regressive
deformation trends. Blasting activity in the lower
benches of the pit were also monitored using
virtual points to provide geotechnical peace of
mind. Using SSR-Viewer’s intuitive visualisation
tools, the geotechnical team could pinpoint
hotspots of movement across the pit,
62 International Mining | AUGUST 2019
Geobrugg’s line of defence at Kanmantoo
The Kanmantoo Copper Mine in the Adelaide Hills of South Australia is operated by Hillgrove
Resources Pty Ltd. Underground Cornish style mining occurred in the area in the mid 1800s. The
first open pit became operational in the 1970s, and then more recently the mine was reopened in
2011. Since then Geobrugg has worked closely with Hillgrove Resources, by designing and
supplying a range of systems. Two smaller pits (Kavanagh and Spitfire) were operational from
2011 to 2015, before amalgamating into one. The result is the Giant Pit.
Its steep-walled design requires an intensive rockfall management plan and the installation of
extensive rock support. The pit has two main competent rock types; biotite Schist (BSch), and
garnet andalusite biotite schist (GABS). There are no major faults and few shear zones, so the
stability of the pit is defined by four main joint sets. Two steep easterly dipping structures result
in planar and wedge failure modes, mainly on the western walls.
Geobrugg has worked closely with the mine and the installation contractor to manage a range
of rockfall hazards. To date, approximately 45,000 m² of DELTAX®, MINAX® and TECCO® drape
mesh have been installed, along with over 1,000 lm of low (35 kJ) and high energy (3,000 kJ)
rockfall barriers, and 300 lm of attenuators.
Pre-splitting of batters, mechanical scaling and hydro-washing are used to reduce and
eliminate the potential for general, smaller rockfalls. General weathering, rainfall, and blasting
have still lead to rockfall events, so
engineered structures such as
rockfall drapes and low energy
barriers (T35) are installed to
manage these in selected areas.
Large scale wall failure is
managed by a slope stability radar
and three laser scanners. Due to the
potential for rapid, brittle type
failures and orientation, batter
instability is difficult to predict and
alarm with radar and scanners.
Hence this risk has been managed
Geobrugg has worked closely with the mine and the
through berm retention (using shear
installation contractor to manage a range of rockfall
hazards
pins), and high energy rockfall
barriers. In areas where berm loss has still occurred, Attenuators are installed to mitigate the
additional rockfall risk.
Mining operations ceased in May 2019 and the pit is now being redeveloped into a pumped
hydro project though scheduled to be completed during May, but treatment of ore stockpiles will
continue until mid-2020. Hillgrove is now evaluating a possible underground mining development
below the Giant Pit, that may be able to work in conjunction with the Pumped Hydro Energy
Storage (PHES) development.
represented visually through a colour gradient
heatmap which was draped over the top of a
photographic representation of the area. The
geotechnical team were also able to perform a
velocity analysis and even conduct remote
inspections of the areas of interest in real-time
using the GMS-Dual’s built-in telescopic camera.
Additionally, the system’s ability to monitor both
prism and virtual prism points allowed the
geotechnical team to monitor the remaining
prisms installed on the pit walls, providing three-
dimensional displacement data of these points in
real-time. “Thanks to the GMS-Dual and its
prismless monitoring, we have been able to
counteract the lack of continuous, real-time
slope monitoring caused by the unauthorized
removal and vandalism of physical prisms by
intruders,” says Peter Alip, Chief Geotechnical
Geologist, Masbate Gold Project. “Moving
forward, our geotechnical team is excited to
incorporate the system into our permanent on-
site monitoring processes and procedures thanks
to its easy setup, user-friendliness and smart
data capture. We are eager to continue using the
GMS-Dual for effective slope stability in order to
detect hazards early, make confident decisions
and manage risk, without having to rely solely on
physical prisms.”
GroundProbe and tailings dam
monitoring
Mines are fast beginning to adopt monitoring of
tailings dams as a necessity following highly-
publicised tailings dam failures in recent years.
The risk of loss of life, decreased productivity,
environmental impacts and reputational impacts
are all strong motivators for mine owners to
implement and adopt tailings dam monitoring.
The recent failures has also brought on pressure
from investors for the large corporates and