Applying Distributed, Coupled Hydrological Slope-Stability Models for Landslide Hazard Assessments
Abstract
Application of distributed, coupled hydrological slope-stability models requires knowledge of hydraulic and material-strength properties at the scale of landslide processes. We describe results from a suite of laboratory and field tests that were used to define the soil-water characteristics of landslide-prone colluvium on the steep coastal bluffs in the Seattle, Washington area and then use these results in a coupled model. Many commonly used tests to determine soil-water characteristics are performed for the drying process. Because most soils display a pronounced hysteresis in the relation between moisture content and matric suction, results from such tests may not accurately describe the soil-water characteristics for the wetting process during rainfall infiltration. Open-tube capillary-rise and constant-flow permeameter tests on bluff colluvium were performed in the laboratory to determine the soil-water characteristic curves (SWCC) and unsaturated hydraulic conductivity functions (HCF) for the wetting process. Field-tests using a borehole permeameter were used to determine the saturated hydraulic conductivity of colluvial materials. Measurements of pore-water response to rainfall were used in an inverse numerical modeling procedure to determine the in-situ hydraulic parameters of hillside colluvium at the scale of the instrument installation. Comparison of laboratory and field results show that although both techniques generally produce SWCCs and HCFs with similar shapes, differences in bulk density among field and lab tests yield differences in saturated moisture content and saturated hydrologic conductivity. We use these material properties in an application of a new version of a distributed transient slope stability model (TRIGRS) that accounts for the effects of the unsaturated zone on the infiltration process. Applied over a LiDAR-based digital landscape of part of the Seattle area for an hourly rainfall history known to trigger shallow landslides, the model computes a factor of safety for each grid cell at any time during a rainstorm.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.H54B..06G
- Keywords:
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- 1810 Debris flow and landslides;
- 1875 Vadose zone