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Keywords: Slope stability, tailings dams, limit equilibrium methods, reliability analysis,
Monte Carlo simulation
The stability of an embankment is a vital consideration in tailings dam design,
construction and management. A general overview of dam construction methods, potential
failure mechanisms for tailings dam embankments, and different methods of analysis
including deterministic and probabilistic analyses are included in this thesis.
Deterministic analysis includes a discussion of the stability of tailings dam
embankments by analysing the factors of safety using unique values of each soil, and
geometric, property. The factor of safety is calculated using stability charts (Taylor (1948),
Bishop and Morgenstern (1960), and Spencer (1967)), and limit equilibrium methods such as
those by Fellenius (1936), Janbu (1954), Bishop (1955), Morgenstern and Price (1965), and
Spencer (1967). A parametric study and sensitivity analysis were performed to elucidate the
effects of varying the shear strength parameters and embankment geometry on the stability of
an embankment. Probabilistic methods of analysis use random variables in place of
deterministic values to find a range of factors of safety that describes the inherent variability
in both the soil and geometry in the tailings dam. A first order, second moment, (FOSM)
analysis and Monte Carlo simulations were performed to describe the factors of safety in a
risk analysis-based context.
The deterministic and probabilistic methods were applied to simple baseline cases and
a case study of an existing tailings dam using hand calculations performed in Microsoft
Excel™, and GeoSlope SLOPE/W 2012 software. The embankments were analysed under
both short- and long-term conditions (i.e. in terms of both total and effective stress
parameters), with the effects of pore water pressure and horizontal seepage considered.
This research found that there were advantages and disadvantages to both the
deterministic and probabilistic methods of analysis. The deterministic methods were generally
easy to use but the input variables were single values which may not accurately reflect the
anisotropy or inhomogeneity within the soil in the tailings dam embankment. This could
produce factors of safety that are not representative of the entire embankment. On the other
hand, probabilistic analyses took into account such anisotropy and inhomogeneity, but
required a more detailed understanding and analysis thereof. It was found that deterministic
methods of analysis were suitable in calculating factors of safety, however it is also beneficial
to perform probabilistic analyses to find the factor of safety and refined safety margins when
the variability from uncertainties is included.