The pre- and post-failure deformation behaviour of soil slopes

Abstract

This thesis examines the pre and post failure deformation behaviour of landslides in cut, fill and natural soil slopes, and of the deformation behaviour of embankment dams. The deformation behaviour of landslides and embankment dams have been analysed from a database of case studies from a number of classes of slope (and dam) and material type. The database included some 450 landslides in cuts, fills and natural slopes, and some 170 embankment dams.

For landslides in soil slopes, methods and guidelines have been developed for use in the analysis, evaluation and prediction of the pre and post failure deformation behaviour. They take into consideration the factors influencing and the mechanics controlling the deformation behaviour for the classes of slope and material types, which are different for pre and post failure. Pre-failure deformations are largely controlled by the effective stress conditions within the slope, changes in the boundary conditions and the response of the soil to those changes in boundary conditions. Whether the soil, under the effective stress conditions imposed within the slope, is contractive (and saturated or near saturated) or dilative on shearing, has a significant influence on the pre failure deformation behaviour. The post failure deformation behaviour is strongly influenced by the mechanics of failure (including whether the soil is contractive or dilative on shearing), the source area slope angle, the downslope geometry, the orientation of the surface of rupture, the material properties and slide volume. Guidelines are presented for prediction of 'rapid' and 'slow' post failure velocity.

For embankment dams, methods and guidelines have been developed for evaluation and prediction of the deformation behaviour during and post construction for selected embankment types. They take into consideration the influence of material type and placement methods, material strength and compressibility properties, embankment zoning geometry, embankment height, and reservoir operation, amongst other factors. Guidelines have been developed to assist in the identification of 'abnormal' deformation behaviour, which can be related to internal deformations or a marginal stability condition and the onset to failure.