OPERATIONS •
Barnabas Mboweni
In the confines of the man-made underground caves and mining pits,
water is continually intruding through fissures, seepage, rain, and even
accidental at times from pipe burst and leaks from service lines.
inspection of the cave will rely on the timely completion of the
mine dewatering activities.
Critical considerations
As a starting point, various considerations must be undertaken,
most critical of these will be:
1. The vertical distance between the highest point discharge
line on surface and the lowest point to be pumped
underground.
2. The rate at which the mine is to be de-flooded (currently
expected to be around 1 000 cubic meters per hour;
enough to fill an Olympic-size swimming pool in 2.5 hours).
3. Available power at the site. These factors will determine the
method to be used, discharge pipe sizes, which at a depth
of 1 024m, would require a pipe capable of handling over
100 Bar (10MPa) without taking into account any friction
head losses through the line. This is close to 100 times the
normal atmospheric pressure at sea level (101.325 KPa).
Fortunately, the mine (Prieska) is equipped with both a vertical
shaft and a series of declines running all the way to the bottom
level of the mine. This allows for a few viable options that can be
considered for the dewatering of the mine. The 400m landing
stations along the decline also provide the perfect opportunity
for intermediate pumping stations to form a cascading system.
This can reduce the pumping heads to about 40 Bar per station
instead of over 100 Bar from the bottom straight to surface.
First option would be to go through the vertical shaft. This
would entail the use of submersible turbine multistage pumps
www. africanmining.co.za
African Mining Publication
African Mining
African Mining • May 2020 • 41