Environmental Engineering Reference
In-Depth Information
water level of a TSF could result in an overl ow. Lack of adequate operational control
can ultimately result in a structural failure.
3. Equipment failures refer to the failure of mechanical equipment such as pipelines,
pumps, or valves used for tailings management. Burst pipelines, coupling breakage and
pump failure are common causes of accidental discharge. Equipment failures are usu-
ally less serious than failures due to operational or structural causes but can nevertheless
cause signii cant harm to the environment, and reputational damage to the operator.
4. Unforeseen consequences of tailings placement may occur. Some instances of damage
to the environment are the result of simple oversight in the design, operational proce-
dures or closure of a TSF. For example, the long-term consequences of slow seepage
from the base of a TSF may not have been adequately considered at the design stage
and may not become apparent for some years.
Many of the past failures occurred in poorly engineered storages, constructed before tailings
dam design standards were developed. However, failures continue to occur and, increasingly,
it is embankments designed and constructed in accordance with internationally recognized
methods and standards that are failing. According to UNEP (2001), 'the number of major
incidents continues at more than one a year'. Modern tailings embankments are designed in
accordance with the same principles as water storage dams, and involve comparable levels of
investigation and construction control. However, it is clear that the proportion of failures in
tailings storages is much higher than in water reservoirs ( Case 18.4 ). Added to these failures,
are many smaller incidents that cause serious environmental damage.
The number of major incidents
continues at more than one a
year.
CASE 18.4
How Safe are Tailings Dams?
While it appears that the mining industry has the knowl-
edge to design dams safety, can it be said that all dams
are built to the same standards, with state-of-the art tech-
nology and management? Some are better than others, and
failures have occurred. Several recent studies have been
conducted to compile data on tailings dam failures, isolate
the causes of these failures and identify trends. No single
legislative body, however, records tailings dam statistics.
Furthermore, the data do not allow comparisons between
the number of tailings dam failures and the total number
of tailings dams built in any given area or time period.
However, comparisons have been made between tailings
dam failures and incidents at hydroelectric and water-
retaining structures. Although the database is incomplete,
some convincing trends have emerged. The chart shows
a plot of the total number of failures reported for all
countries in 10-year increments for both tailings dams and
water supply dams. Before the 1940s, there were very few
reported failures of tailings dams, either because many of
the existing dams ware not documented, or because the
total number of failures was small. From the 1940s to
the 1970s, the number of failures for both tailings dams
and water supply dams increased substantially. The rise in
the number of failures in the 1950s to 1960s may have
been due to the increasing size and weight of earthmoving
equipment. This trend peaked in the late 1960s for water
supply dams, and in the 1970s for tailings dams. The
overall behaviour of the two structure types is, in general
terms very similar.
Source: UNEP 2001.
45
44
40
35
30
27
27 27
25
26
22
20
19
18
15
14
10
8
8
8
7
7
5
0
6
2
1
1
1
0
1909
1919
1929
1939
1949
1959
1969
1979
1989
1999
Tailings Dam Failures (123 Total Cases)
Water Supply Dam Failures (151 Total Cases)
 
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