Since 2002, potential failure modes analysis (PFMA) using qualitative or semi-quantitative methods have been established to systematically identify, describe, and evaluate the ways in which a dam or its appurtenant structures could potentially fail. Probabilistic slope stability analysis was first introduced in the 1970s. Probabilistic slope stability analyses allow uncertainty to be quantified and incorporated rationally into the PFMA by providing a range of factors of safety with their associated probability. In deterministic slope stability analysis, the engineer or the engineering team select arbitrary material properties for the slope stability model based on their experience and their engineering judgment. There are no widely used guidelines on how these engineering properties should be selected. The probabilistic analysis is a risk tool to allow the PFMA team collectively decide on how the uncertainties in the slope stability analysis be addressed. This paper presents a case study of two slope stability analysis scenarios for a hydroelectric dam located in Colorado using deterministic and probabilistic methods. The probabilistic slope stability analyses were performed using the limit-equilibrium and a finite-element methods. The advantages and disadvantageous of using the probabilistic method in the PFMA are discussed.
