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.

INTRODUCTION

Mining operations in open pit mines produce progressively deeper pits. These structures account for a large portion of the world's mineral production (Wyllie and Mah, 2004). With the widening scope of mineral applications, their demand is driven by an ever-growing population (Lusty and Gunn, 2015). The United Nations (2015) projected a global population increase of more than 1 billion within the next 15 years; an increase from approximately 7.3 billion in the year 2015 to 8.5 billion. The imminent future thus carries the mineral industry into even more precarious environments in order to accommodate this demand (Lusty and Gunn, 2015). With increasing depths comes increasing risks of slope failure and it is thus essential to rigorously manage the hazard associated with rock slope stability. Fortunately, the advancement and increased utilization of computational tools now allows mine personnel to make improved informed decisions (Hochbaum and Chen, 2015). With increasing depths and associated stresses, Stacey et al. (2003) emphasized the importance of numerical stress analysis methods and Hoek, Rippere, and Stacey (2000) promoted the undertaking of numerical modelling, particularly for more complex slopes or lithologies where limit equilibrium analyses are often too simplistic.

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