SLOPE STABILITY MONITORING
areas including inaccessible and unsafe areas can
be covered. Discontinuity properties including
orientation, spacing, surface roughness and
persistence can be determined remotely and
accurately over long distances.
The scans are imported into Maptek
PointStudio software for analysis. Scans can all be
georeferenced at the same time, and after filtering
of trucks, vegetation, snow or dust, a complex 3D
surface is created for geotechnical mapping.
Various methods for extracting discontinuity
data are used, including automated techniques
that examine orientation trends and a semiautomated
method that depends on user structural
interpretations of specific features. Manual point
cloud analysis gives the geotechnical engineer the
same control as in the field, with the benefit of
unrestricted data coverage.
On the other hand, the automated method is
quick, uses more detailed data and reduces the
potential bias of the geotechnical engineer. Every
visible joint plane is assessed and characterised.
The orientations of the geological defects are
then plotted on the stereonet to analyse and
determine discontinuity orientations and major
joint sets. The data can also be exported as a csv
file into rock mass analysis software.
PointStudio geotechnical tools allow for
accurate measurement of surface roughness. The
selected surface is divided into grids depending
on user preference. The results are then used to
determine the joint roughness coefficient (JRC).
Data from one Letšeng pit was used for
kinematic analysis to determine possible modes
of failure, by analysing the relationship between
the major joint sets/planes of individual joints, the
slope and the basic friction angle. The results
indicated that possible localised failures are
restricted to bench scale and inter-ramp failure is
not likely. The data can be used in limit
equilibrium and numerical modelling packages for
detailed slope stability analysis.
Mapping of blast blocks is vital for blast design
to minimise highwall damage and to achieve
controlled and desired fragmentation. At Letšeng,
highwall control is of high priority because of the
recently implemented steep slope. Every trim
block is mapped and geological information is
analysed for geological defects and rock mass
strength. PointStudio can extrapolate joints
throughout the trim blocks to predict blast
integrity.
Open pit mining best practice calls for timely
detection of potential rock slope instabilities and
effective management of identified instabilities,
making both strategic and tactical slope
monitoring an integral part of any mine program.
Letšeng deploys prisms for long-term
deformation monitoring, radar in critical areas for
tactical monitoring, and the XR3 laser scanner for
hazard identification, strategic and tactical
monitoring.
A Maptek XR3 laser scanner is used at the
The scanner is used for both periodic and
Letšeng Diamond Mine to acquire point cloud
data for geotechnical analysis, volumetric
continuous slope monitoring. Scans must be calculations and rockfall assessment
taken from a fixed point for periodic monitoring,
so beacons are constructed strategically around performed on the crest above where it has been
the pits. Scans are imported into Maptek Sentry compromised beyond an allowable 10 m. Overall
office software for data processing and analysis. slope compliance is assessed in PointStudio
Continuous monitoring is conducted using where cross sections of the actual slope are
Sentry field software hosted in the Sentry DMS overlain on the designed slope.
system in a deployable trailer. The DMS comprises Maptek states: “Since acquiring the Maptek
a Maptek XR3 laser scanner, built-in tripod, solar XR3 laser scanner geotechnical engineers at
panels, weather station, standby generator and Letšeng can collect significantly larger datasets
Wi-Fi antenna mast for communications. Scans are more safely. The smart PointStudio geotechnical
downloaded automatically into the built-in
tools are used to characterise geological defects
computer for processing.
and determine possible failure modes. Sentry
Output data includes displacement, velocity, technology is applied in slope deformation
moisture intensity and inverse velocity time
monitoring as well as mining compliance
graphs The behaviour of each graph can be
measurements. Management can now make more
related to environmental factors such as rainfall, informed safety-related decisions based on slope
wind direction and intensity. Trigger alarms can be behaviour.” IM
set and notifications sent
through local mine
networks.
Benches are the
fundamental building www.geobrugg.com/mining
blocks of the pit slope
and their geometry and
behaviour often controls
the inter-ramp and hence
the slope design.
Letšeng has
implemented rigorous
quality control and
quality assurance on the
highwalls to ensure that
the required catchment
is achieved.
The 3D point cloud
data is used to compare
the actual slope to
design, which quantifies
the frozen toes as well
From SPECIFIC surface support SAFETY to rockfall SOLUTIONS protection
as crest damage. Crest
FOR THE MINING INDUSTRY
SPECIFIC SAFETY SOLUTIONS
compliance is calculated
by comparing actual and
FOR THE MINING INDUSTRY
design crestline, while
toes are determined by
comparing the actual
bench face with design.
Geobrugg AG | CH-8590 Romanshorn | www.geobrugg.com
Intensive rock barring is
JULY/AUGUST 2020 | International Mining 77