• OPERATIONS
dropped down the vertical shaft. Temporary skid mounted
intermediate pumping stations would be installed at each 400m
decline landing. The submersible pumps would then discharge
into these stations. The stations would then cascade up to the
surface.
Possible drawbacks
Two main drawbacks exist with this option:
1. Serious lifting gear needs to be installed at the shaft to
carry the combined weight of the pumps, power supply
cables and piping with a full column of water.
2. The piping and cables will be continually extended as the
level drops. This means a lot of activities will be taking place
at the shaft on a limited working platform. This makes for
very high safety risks, especially when taking into account
the pressurised pipes that the team will be working with.
Another, perhaps better option, would be to go through the
decline shaft. This provides ample space to hang pipes and
cables; the pipes are also easily accessible for extensions as the
level drops. The cascade system will still be applicable even
with this method to keep the line pressure around 40 Bar. With
4 declines available pumps can be installed in each decline to
accelerate the dewatering rate. Common intermediate stations
would still be used; however, these stations would need to be
sized such that they can accommodate the combined flow rate
of all the face pumps.
This would be the most effective method and all work would
be carried out along the roadway. One additional consideration
to be made with this option is provisions to manage accidental
water resulting from events such as pipe burst. Because the
discharge pipes run along the decline, should a pipe burst, a lot
of silt will be washed off along the roads and carried along with
the water to the lowest point. Recovery from such an event can
be a tedious muddy process if not planned for in the dewatering
strategy.
Previous successful projects
Pumpquip has carried out numerous projects such as this for
a number of clients. Most recent was at an Implats operation,
Marula Platinum Mine, close to Burgersfort in the Mpumalanga
province of South Africa. The original scope was to recover the
silt settling system underground and to refurbish and optimise
the main pump station. On arrival we were requested to recover
two declines with numerous interconnecting crosscuts, all
“ The cascade system
will be applicable even with
this method to keep the line
pressure around 40 Bar.
Leon Louw
At Orion Minerals’ Prieska Copper and Zinc project in the Northern Cape province of South Africa, the historic shaft
has been submerged for a number of years.
42 • African Mining •May 2020
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