Rupture Failure Modes in Analyses of Stability of Soil and Rock Slopes

Methods of stability analyses of slopes, such as limit analysis or the limit equilibrium method, require postulation of the pattern of failure and the mode of material yielding. They typically do so by assuming the shear-type material failure (mode) along kinematic discontinuities (pattern). Observations of slope failures, however, lead to the conclusion that both soils and rocks often display a rupture-type mode of failure with large separation components of displacements, in addition to the shear-type failure. Such modes are observed, for example, as opening cracks at the crest in early stages of slope failure and as blocks separating from one another, giving rise to toppling failures. The shear strength of rocks is typically represented by a non-linear strength envelope, whereas soils are more commonly described with a linear function of normal stress. The role of the strength envelope and the plastic flow rule will be discussed in the context of rupture modes in slope failures. Examples of slope analyses with geomaterial rupture will be shown with a focus on the safety assessment of slopes. It will be demonstrated that neglecting rupture modes in stability analyses may contribute to overestimating the slope safety.