Predicting rainfall-induced slope instability

The problem discussed in this paper is that of shallow slope failures caused by infiltration of water. These failures usually occur in regions of the world where steep slopes consisting of residual soils are subjected to periods of prolonged and heavy rainfall. A mechanism for the failure of these slopes is postulated whereby in situ soil suctions are decreased by the ingress of a wetting front until a critical depth is reached where the shear strength of the soil is no longer sufficient to ensure stability. A technique for predicting whether a particular rainfall event (defined in terms of intensity, duration and return period) will cause ingress of a wetting front to this critical depth is discussed, with particular reference to the failure of a number of road embankments in the Northern Province of South Africa.