Influence of spatial variability on 3D slope failures

This paper considers the influence of spatial variability of undrained shear strength (c(u)) on the stability of long slopes cut in clay. Random fields of c(u) are mapped onto finite element meshes used in Monte Carlo analyses, and slope performance is quantified in two ways: (a) reliability is computed as a function of the global factor of safety, F (based on the mean property value); and (b) volumes of material associated with potential slides are discussed with respect to the probability of failure. By plotting contours of displacement and shear strain invariant at failure, slide volumes are shown to be influenced by the depth-dependency of the statistics of c(u) in 2D analysis and, additionally, by the type of failure mode in 3D analysis. Spatial variability can occasionally result in slope failure at relatively high values of F, although the associated risk may then be relatively low due to the greater likelihood of more localised failure.