The factor of safety against failure, which is the result of a slope stability analysis, can be determined using deterministic or probabilistic approaches. In deterministic methods, the geotechnical parameters (model's inputs) are single, crisp values, resulting as well in a unique value for the corresponding factor of safety. Currently, the risk assessment of a slope failure can be done using a probabilistic approach, generating random values and assuming a particular probability density

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... for the geotechnical parameters of interest. This article aims to develop and implement a methodology for assessing the risk of slope failure in earth dams, using fuzzy number arithmetic, as an alternative to probabilistic methods. To validate the proposed method, the authors used the case of Olho d'Água dam, built in the State of Ceará, Brazil. The results showed that the application of the concepts regarding fuzzy numbers in assessing the risk of slope failures is possible and that this methodology can encompass the uncertainties inherent in the geotechnical parameters on the results of slope stability analyses. The obtained results also showed that the use of probabilistic methods underestimated the risk of failure in Olho d'Água dam. Moreover, the application of this proposed methodology can be extended to other methods of slope stability analysis, arising as a simpler alternative, which takes less computational time than is required by probabilistic approaches.