Environmental Engineering Reference
In-Depth Information
50
40
30
20
10
0
0
50
100
150
Su Vane Strength, kPa
Figure 19.16.
Vane shear test results - Newman tailings.
of the degree of overconsolidation of the tailings. This can be done by taking undisturbed
samples of the tailings and carrying out oedometer consolidation tests.
Alternatively, if consolidated undrained triaxial tests with pore pressure measurement
are carried out on undisturbed samples of the tailings, the pore pressures developed dur-
ing shearing can be measured and the Skempton A
f
at failure determined. Then the
undrained strength can be determined using Equation 6.17, Chapter 6.
The undrained strength of fine silt and clay tailings
in situ
may be measured using a
vane shear. However the results are often very scattered because of the varying degrees of
overconsolidation within layers which have been partly desiccated and the presence of
sandy layers which lead to overestimation of undrained strength. Figure 19.16 gives some
results from the Newman tailings, which show the wide scatter and apparent lack of rela-
tionship to water content.
Where tailings are consistently fine grained, e.g. well away from the discharge point
and not affected by desiccation other than in a single drying phase, reasonably constant
strengths can be obtained by a vane shear.
Swarbrick and Fell (1991) used vane strengths in the laboratory to develop a relation-
ship between undrained strength and water content. Here some consistency was possible,
with good comparison with single stage desiccation in the field. The laboratory tests were
done using a miniature vane, with samples dried in glass beakers.
19.5
METHODS OF CONSTRUCTION OF TAILINGS DAMS
19.5.1
General
In most cases the basic requirements for a tailings disposal area are to store the tailings
in such a way that they remain stable (i.e. there are no slope stability problems) and do
not impact excessively on the environment by water pollution and/or wind and water
erosion. Only in some cases is it necessary, or desirable, to store water in the tailings dis-
posal area.
This should be kept in mind when designing a tailings embankment and one should not
always feel it necessary to construct “a dam” to store the tailings.
Many of the principles and practices developed in conventional water dam engineering
are applicable to tailings, but it should not be assumed that all water dam technology or
philosophy is applicable.
