Abstract：Slope stability assessment is a difficult geotechnical problem because of the uncertainty involved. These uncertainties possess both randomness and fuzziness. Historically，all uncertainties were assumed to follow the characteristics of random ones. However，some uncertainties，especially those based on incomplete information，cannot be handled satisfactorily by the classical random analysis；and in this case，using a fuzzy number to reflect the uncertainty is reasonable. In this paper，a fuzzy point estimate method is presented for the reliability analysis of rock block incorporating block theory and fuzzy sets. As a typical example，it is applied to the stability analysis of a key block in high slope of the permanent shiplock of the Three Gorges Project. Furthermore，it is compared with the fuzzy possibility approach showing that the results by the two methods are essentially consistent. However，the fuzzy possibility method only considers the ambiguity of limit state function and doesn¢t take into account the fuzziness of mechanical parameters. The fuzzy point estimate method provides an effective approach to solve this problem and it can reflect the real situation better because it uses fuzzy-based disposal to every mechanical parameters.
