Approaches to Waste Rock Disposal - Mining and the Environment: From Ore to Metal - page 774

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Restoring original landform Mesa

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Single Terrace or Bench Multiple Terrace

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Break-Away Mound

Photo: Courtesy of Jim Wark, www.airphotona.com

FIGURE 19.6
Types of Landforms Created by Waste Rock Storage

of the storage, if located on a steep slope. In some cases, it may be necessary to excavate one
or more keys so that the waste rock is in contact with sound foundations. Detailed design
is then undertaken to configure the shape of the storage in accordance with its intended
future land use. The design also needs to provide the required characteristics to facilitate
drainage, erosion control and rehabilitation.
Table 19.2 shows the types of land use that can be carried out on different slopes. As can
be seen from this table, low slope angles are preferred for most land uses and are essential
for some. However, the selection of slope angle requires tradeoffs between slope and other
factors. For example:
● Lowering the slope angle increases the overall footprint;
● Lowering the slope angle usually increases the construction effort, increasing the over-
all cost;
● Lower slope angles mean longer slopes which increase runoff volumes, possibly
increasing the need for erosion controls, and
● Lowering the slope angle increases the area to be revegetated.
If infiltration of rainfall is to be encouraged as is often the case in arid situations, concave
surface configurations, pitting or 'moon-scaping', and berms sloping back into the overall
slope are used (Lindbeck and Hannan 1998). If, on the other hand, infiltration is to be
minimized as may be required in wet tropical areas, convex surfaces and berms sloping
outwards may be used to promote runoff. Whichever approach is adopted, it needs to be
supported by an appropriate drainage network. The drainage density and drain designs
are based on calculations of runoff, based on rainfall intensities, catchment areas, slopes
and infiltration capacity. As the drains are located on more or less erodible materials, lin-
ing may be required to provide protection against scouring.

A geotechnical investigation
should be carried out to assess
foundation characteristics
and the need for foundation
treatment prior to dumping.

Whichever approach is adopted,
it needs to be supported by an
appropriate drainage network.