INTEGRATED ROCK SLOPE DESIGN TOOLS FOR MANAGEMENT OF ROCKFALL RISK

Common rock slope design policies reflect models treating rock slope stability as a series of events falling along a continuum of physical triggers, with higher-energy triggers causing larger events. Policies emerging from this conceptualization may be applied to ideal slopes, for which global slope stability is the only hazard being addressed, geological structure is well-understood, triggering events may be predicted with high confidence, and where engineering methods may be implemented to minimize impacts of the resulting events. In such cases, slopes may be inventoried, and triggering events predicted, such that a reactive, asset-focused management policy can be developed. Such a policy forces the assumption of a population of ideal slopes and conditions and allows management only of ideal slopes under ideal conditions. However, globally-stable slopes still present sub-global (rockfall) hazard due to complex structure, varying lithologies, poor past blasting practices, or tectonic deformation, as well as ongoing weathering. Policy designed for ideal slopes and conditions will inevitably fail, resulting in unanticipated rockfall and unmanaged risk. New data on rockfall patterns in the Virginia Valley and Ridge reveal that a significant aspect of rock slope stability is not triggered by discrete events, but rather that the lithostructure exerts strong control over the slope stability unrelated to obvious triggers: Below some threshold, every slope exhibits a characteristic rockfall signal independent of the slope’s global stability. Recent research allows better quantification of rock slope behavior and shows that common rock mass indices correlate well with rockfall behavior and provide a tool for design. This better understanding allows development of an integrated, phenomenology-based rock slope design and management policy which addresses both global and sub-global rock slope stability, thus lowering both hazard and risk, and creating a more ideal built environment for the travelling public.