EIA-REP-325d-12 _BB_ - 201.09.14.pdf - SAHRA

• All pillars in the panel are uniform size.
The biggest concern undermining watercourses and wetlands is the subsidence or displacement that may occur.
Subsidence can be described as a downward movement of the surface that overlies an underground excavation,
or adjacent to the surface excavation.
The effect of subsidence or displacement can be divided into various types of subsidence namely:
Tilt:
During active subsidence tilting may for examplecause buckling of the building. Windows can crack and doors
can be stuck. After the area has stabilized the structure will return to the vertical position. In the case of
watercourses and wetlands drainage or inlet course might be slightly affected.
Strain:
Two types of strain can be identified, tensile strain and compressive strain. Tensile strain can cause elongation
of a piece of land whilst compressive strain can cause the surface to buckle.
Horisontal displacement:
This type of displacement can cause a section of land to move an x amount of meter. This type of displacement
usually form cracks on the edges.
Sub-surface erosions (Potholes):
Potholes form where cracks formed in the upper rock layers are slowly fill with eroded soil. Eventually, a
subterranean cavity forms in the soil, at the soil rock contact, due to the rock acting as a reservoir for this eroding
soil. When this cavity reaches its critical size, it collapses and results in a pothole on surface.
Sinkhole formation:
This type of subsidence mainly occurs where intersections collapse, and is more common in areas where the
depth of mining is less than 50 meters. In contrast to potholes, these sinkholes are usually wide and deep and
approximately the same size as the intersection underground.
Opencast mining
Opencast mining, using the truck and shovel lateral rollover mining method, will be undertaken. Mining will
commence from the initial box cut. Access to the opencast pit will be via a 17˚ pit ramp. A haul road that will be
extended from the nearby existing road will be used to access the mining area. The underground production is
planned to commence on the West Opencast section and will produce at a rate of 160,000 ROM tons per month.
The proposed Usutu Colliery opencast mining project will be undertaken over an area of approximately 200 ha at
opencast areas, namely: portion 6A, 6B, 6C, 9 and 14. Mining will be conducted by open cast mining method,
using a truck and shovel roll over mining technique. The mining will be outsourced to a suitably qualified mining
contractor. Mining will be undertaken by diesel powered mining equipment in the form of front end loaders,
excavators, haul and dump trucks, water carts and graders.
EIA-REP-325d-11
October 2012
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