Abstract
Slope instability in open pit mining environments present significant safety hazards. The
quality and quantity of geotechnical data often expands over time and may give rise to an
increase in reliability and a corresponding reduction in uncertainty of input parameters.
In this paper, the geotechnical model is built on data obtained from four different
consultants over 15 years, spanning from conceptual study to design. Stability conditions
are investigated through Limit Equilibrium Method and compared to the numerical
analysis using Finite Difference Method. Three critical profiles, based on areas of known
concern, are analysed. Kinematically admissible joint orientations are incorporated as
Ubiquitous Joint models and materials are modelled based on the Mohr-Coulomb failure
criterion. Limit Equilibrium Method results revealed that profile A is the most critical
slope, with a significant probability of planar and wedge failure at set of benches. Safety
factors for overall slope indicate planar failure of profile B, although stable, remains below
the acceptance criteria for the overall slope angle, which opted for numerical analysis.
Profile C was deemed stable and no further analyses were required. There was a good
agreement between methods of analysis, in terms of safety factors and failure surfaces.
Finite Difference Method computed lower safety factors to the point of critical stability for
profile B. A reduction in overall slope angle by 12° for this profile increases the safety factor
to an acceptable value and reduces the probability of failure to 2% from a previous 14%.
The lowered range in probability suggests a reduction in result variability and thus an
increased level of confidence in data and analysis.