An economic risk evaluation approach for pit slope optimization
LF Contreras
In open pit mine design, it is customary for geotechnical engineers to
define the appropriate slope design angles within practical limits. The
conventional approach to slope angle design is based on the comparison of
calculated stability indicators, such as the factor of safety (FS) and the
probability of failure (PF), with generic acceptability criteria not directly
related to the impacts of failure. A major drawback of this type of
approach is related to the difficulty of defining meaningful acceptability
criteria. An alternative methodology of pit slope design is proposed, where
the economic impacts of potential slope failures are calculated and used as
the elements on which to apply the acceptability criteria for design. The
methodology is based on the construction of a graph, referred to as a risk
map, that relates the probability of exceeding the economic impact of slope
failure to the magnitude of the impact measured in monetary terms. The
process includes the analysis of a selected number of representative years
of the mine plan and slope sections of the pit areas to define the required
inputs for the construction of the risk map. The paper discusses the
concepts used in interpreting the probability of slope failure, and describes
the approach followed for the estimation of the economic impacts of slope
failure and the construction of the risk map. Finally, the two main uses of
the risk map are discussed, including the comparison with acceptability
criteria for the evaluation of a specific open pit design and the comparative
analysis of open pit design options in terms of value and risk to identify
optimum pit layouts.
Keywords: risk evaluation, economic risk map, slope design, slope failure, probability
of failure.