Landslide Hazard Rating for the Oregon Coast Range

by Edward R. Burroughs, USDA, Forest Service, Intermountain, Forest & Range Experiment, Station, Moscow, ID, USA,

Document Type: Proceeding Paper

Part of: Watershed Management in the Eighties


The landslide hazard rating system for shallow soils on steep terrain over hard sandstone has three components: ground water response to precipitation, soil shear strength (including root strength), and a factor of safety model. Ground water rise over a hyperbolic-shaped bedrock surface in debris avalanche terrain is empirically derived as a function of easily measured site characteristics. Data on soil shear strength are based on triaxial tests on samples from sites with a high potential for translational failure. Root strength is the sum of the residual strength of Douglas-fir roots as they decline with time after clearcutting and the passive resistance to sliding of an alder soil-root mass. Driving and resisting forces are calculated for a three-dimensional block using estimated ground water rise for a selected design storm, soil shear strength, and estimated root strength.

Subject Headings: Soil strength | Landslides | Shear strength | Geohazards | Public health and safety | Ratings | Sea water | Vegetation | Oregon | United States

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