Despite improvements in recognition, prediction and mitigative measures, landslides still extract a heavy social, economical and environmental toll in Switzerland. Recent landslides experienced in the Swiss Alps demonstrate the need for a deeper understanding of the geological and physical processes leading to catastrophic slope failure. Large-scale rockslides (e.g. Randa, Sandalp, Goldau, Elm, etc.), illustrate the destructive potential of these mass movements and the need for further study to improve our comprehension of the mechanisms involved. Advances in rockslide hazard assessment and forecasting will only be made when the mechanisms responsible for the evolution of catastrophic failures are better understood.

To date, the study of landslides (or more specifically within the framework of this proposal - rockslides) has been largely descriptive and qualitative. Studies that do focus on some quantitative aspect of large-scale mass movements are often limited to individual mechanisms or triggering processes. Traditional treatments have pursued phenomenological based approaches where a two-dimensional slide plane is assumed or delineated from survey or air photo data, and a back analysis is performed to determine the conditions existing on the surface at failure. In other words, the analysis of unstable rock slopes has largely focused on the back analysis of stability along a fully developed failure plane, without considering how the failure plane evolved.

In this proposal, we aim to study the evolutionary failure processes leading to large-scale mass movements in massive hard/brittle rock slopes. The working hypothesis of the project contends that rock slope instability occurs through a process that involves the progressive development of a failure plane along a path that passes through existing discontinuities and intact rock bridges, either in a planar or stepped-path fashion. These developments involve a complex process of fracture nucleation, propagation and coalescence, combined with spatio/temporal variations in pore pressures.

Rock slope failure through interacting discontinuities and intact rock bridges.