Over the last years, it has become increasingly popular to include both deterministic (i.e., Factor of Safety) and probabilistic (i.e., Probability of Failure) methods in defining acceptability criteria for the design of operating mines and mining projects in Chile. There are many different methods available to calculate Probability of Failure, and each has its advantages and disadvantages. There are methods that are considered more rigorous nevertheless time-consuming to perform, while the less rigorous ones are generally simpler and faster to implement. This paper points out the most frequently used methods for calculating Probability of Failure of rock slopes in Chilean Practice. Among them, there are those that are approximations from Taylor Series, specifically the First Order Second Moment (FOSM), Monte Carlo and Latin Hypercube, Monte Carlo with Response Surface, and Point Estimate Method. In this paper Limit Equilibrium Modeling was chosen to develop a comparative analysis among the reliability methods in a hypothetical slope comprised of Mohr-Coulomb materials and a simplified rock slope from a Chilean mining operation.

1. Introduction

Deterministic methods have been the classic approach in the assessment of slope stability and remain applicable because of their simplicity and ease of interpretation. Nevertheless, probabilistic methods have gained a place in geotechnical engineering, due to their ability to explicitly incorporate the uncertainty of properties, loads and analysis tools. As is established by Christian (2004) [1], the Factor of Safety is a value computed by well-known methods that provides a measure of the expected performance of a slope. Reliability theory does not invalidate such calculations; it extends them by giving them a context and additional information to help engineers interpret the results.

Geotechnical design of open pit slopes requires acceptability criteria which define what is permissible or not. These criteria are commonly defined in terms of a minimum permissible Factor of Safety (FoS), and/or a maximum permissible Probability of Failure (PoF).

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