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Soils are inherently variable: even within an engineered, constructed, embankment, the
material is potentially anisotropic and inhomogeneous. This is especially true for tailings
dams where the embankments are generally constructed, in stages, from borrowed fill to
increase the available storage as the level of the impoundment rises. In contrast to a
deterministic analysis, probabilistic analyses treat the input parameters as variables that
change according to an assigned probability distribution function. This sets the factors of
safety in a risk-based context to represent the variability in the soil profile.
Here, the factors of safety were calculated using both deterministic and probabilistic methods
of analysis: they were then used to determine the most suitable prediction of the stability of
tailings dams embankments.
Problem definition
There is extensive literature available that relates to slope stability and includes coverage of
both limit equilibrium, and probabilistic, methods. In the past, deterministic analyses allowed
the design process to be simplified by neglecting uncertainties in the model, compromising on
various critical and realistic features of the embankment that would affect the stability. Since
potentially threatening uncertainties are not considered, many embankments have failed that
were designed and deemed ‘safe’ according to deterministic methods of analysis. Probabilistic
methods of analysis have been difficult to adapt into routine analysis due to their complexity,
and the presupposed knowledge, time, and effort required to perform the analysis and
interpret the results. There is an ominous need for further understanding of probabilistic
modelling to design and analyse the stability of embankments to help militate against failures
in the future.
The task of analysing stability has become relatively easy due to the increased knowledge
gleaned from the lessons of previous tailings dam failures and the increased availability of
easy-to-use software (e.g. @RISK and SLOPE/W). However, there is a downside to making
the process easy; the geotechnical fundamentals can often be overlooked, which could lead to
misinterpretation of the results with unknown consequences for the ultimate safety of an
embankment. This can ultimately put lives and the environment at risk of significant damage
as a result of a tailings dam failure.
The research in this thesis aims to identify whether the factor of safety determined using
deterministic approaches gives a suitable prediction for the stability of tailings dams
embankments. A comparative analysis of the factors of safety calculated using deterministic