Environmental Engineering Reference
In-Depth Information
In many cases it is better to consider tailings embankments as landfills, or dumps of fine
grained soil which have to be engineered to:
- Optimise the amount of tailings which can be stored in a particular area;
- Control piezometric conditions to ensure adequate strength and stability;
- Control the environmental impact.
Australian practice has in the past been (and to a large extent still is) biased towards
constructing conventional dams to store tailings. This approach also applies in some other
countries. This is possibly due to:
- Many designers have a background in water dam engineering;
- Regulatory authorities require such an approach (largely because of their background
in water dam engineering);
-A relatively wet climate in many mining areas and many mines with very fine grained
and/or oxidised tailings which are not readily utilized in “upstream” construction
methods.
There is a recognition amongst many practitioners that this philosophy is costly and
unnecessary and alternative methods are being used.
The following discussion is intended to give an overview of the various alternative
methods and their limitations, with a view to encouraging their consideration and adop-
tion where appropriate.
19.5.2
Construction using tailings
There are three main methods for constructing tailings embankments using the tailings as
a major construction material:
- Upstream method;
-Downstream method;
- Centreline method.
These are described in some detail in ICOLD (1982d) and Vick (1983).
19.5.2.1
Upstream method
The important features of this approach (
Figure 19.17
) are:
-The starter dam is essentially a containing embankment and a support for the tailings
discharge line, rather than a dam in itself. The starter dam is best constructed of per-
meable rockfill (e.g. mine waste) to allow drainage of seepage water and to control ero-
sion. However, it may be constructed of relatively impermeable rockfill, earthfill or
even dried tailings pushed up by bulldozers from the tailings beach.
-Tailings discharge must be controlled by e.g. spigotting to ensure that the coarser sandy
tailings are deposited near the starter dam. This is essential to control seepage pressures
as outlined below.
- The water pond (decant pond) must be kept well away from the edge of the storage. If
allowed to come close to the edge, the piezometric pressures will be high and slope
instability may result, or internal erosion and piping of the starter dam or of the tailings
into the starter dam may occur.
- The coarse tailings are likely to be at a low to medium relative density and, if saturated and
subjected to earthquake, may liquefy, leading to slope failure with a subsequent flow failure
of the tailings. Because of this the method is seldom used in seismic risk areas. It should be
