GEOLOGIC INPUT FOR LANDSLIDE HAZARD MITIGATION

Effective mitigation of landslide hazards requires the engineering geologist to recognize and adequately characterize landslide deposits and landslide-prone topography. This site characterization is necessary to construct an accurate conceptual model of the present and future geologic setting. The model will provide the design engineer the information necessary to evaluate future stability or stabilization schemes, if required.

The author has observed too many landslide-hazard evaluations and investigations that have resulted in an inaccurate conceptual model. This may be due to a number of different factors including sketchy or inadequate geologic data obtained from a poorly designed investigation program, flawed interpretation of the data, a lack of understanding of landslide processes, and/or a lack of understanding of what information is required.

A good conceptual model includes information on water conditions, material properties, appropriate shear strength parameters of the soil/rock mass, topography, material thickness, and discontinuities. It also requires predictions of how these properties might change in the future. Observation of past and present processes at and surrounding a site along with an understanding of slope performance in similar conditions regionally is important. This presentation will show several case studies from the Rocky Mountain region that illustrate how a flawed conceptual geologic model can lead to gross underestimates of risk and overestimates of stability.