Monitoring
The monitoring of tailings dams can
be done on the ground or via remote
sensing methods. Remote sensing
methods would include regular satellite
monitoring, usually on a fortnightly
basis, to monitor slow movement and
more importantly, water and wetting
of the tailings. An increasingly popular
method is the use of unmanned
aerial vehicles (UAVs) or drones
to monitor tailings dams. Ground-
monitoring methods range from
geotechnical instruments (for example
contractometers and extensometers) to
measure the behaviour of the dam wall
and slopes as well as open standpipe
piezometers, or other types of hydrology
sensors, to measuring fluid levels and
behaviour.
Tailings facilities require specialist
input in most instances because of their
safety risk ratings and potential for
environmental and social impacts, says
Ian Hammond of Geotheta. “The basics
of tailings engineering are not complex,
but the magnitude of the facilities
requires dedicated attention to design,
operating, and closure. This covers the
entire life-of-mine cycle and therefore,
regular monitoring is necessary,” says
Hammond. To this end, Geotheta
assists clients in ongoing monitoring,
instrumentation, and real-time
monitoring, as well as ongoing design
verification. “As part of our technical
advances, we are also able to identify
and predict issues by using military-
grade infrared scanning of moisture-
sensitive areas of tailings facilities,”
adds Hammond. “Trials which we have
done on this have provided invaluable
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Tailings dam designs depend on the topography of the ground and the material available to build
it. The tailings dam at Nokeng is located at a higher elevation than the processing plant, and more
powerful pumps are needed to get the tailings to the dam.
movement. Every few years, the level of
the dam typically is raised to keep up
with the mine production. Geotechnical
engineers generally plan out the raises
over the life of the mine, which can be
20 years or more. Keeping excess water
out of a tailings facility is another issue.
Designs will often include diversion
channels to keep surface run-off water
out, because any water that gets in will
be contaminated by metal, sulphides, or
other deleterious minerals and elements
as well as processing chemicals in the
tailings — it is also additional water that
has to be treated and managed. The most
common modes of failure in tailings
facilities are due to rotational sliding,
foundation failure, overtopping, erosion,
piping, and liquefaction.
Mining in focus
The rehabilitation of a tailings dam using mulch.
information and re-assurance to owners
and the appointed professional(s) on a
number of facilities — tailings and water
dams alike,” he says.
In decommissioning a tailings dam,
the engineers and environmental
specialists will reduce the amount
of water behind the tailings dam
to mitigate the need for long-term
management. This is done by contouring
the final surface into the existing
landscape as far as possible. However,
since historical processing methods
were less effective than present
processing methods, an increasing
number of historical tailings dams are
being reprocessed. Alternative tailings
management technologies have been
developed, including filtered dewatered,
stacked deposits; thickened dewatered
systems; frozen tailings deposits; and
paste disposal. b
For independent geological and geotechnical consulting, market studies, reviews,
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please send an email to [email protected] or visit the website,
www.bowlineps.co.za
JANUARY 2019 MINING MIRROR
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