In recently years, number of slope failures with a large-scale have occurred in the mountainous areas and causing a big lost of human lives and properties. The slopes failures are usually occurred after heavy and long lasting rainfall. However, up to now the explanations of mechanism of the rainfall induced slope failures have not been extensively studied. In this paper the mechanism of the rainfall induced slope failures is studied. An example to calculate factor of safety for particular slope in the central Vietnam under rainfall conditions is presented. The results of this study serve as a foundation for explanation of the reduction of negative pore-water pressure, shear strength and then induced the slope failures. Meanwhile, the recover of negative pore-water pressure, shear strength and factor of safety of slope after rainfall stopped are discussed.
