Impact of Diverse Hydrologic Pathways, 3D Failure Geometries, and Unsaturated Soil Suctions on Shallow Landsliding
Abstract
Shallow landslides and ensuing debris flows can be triggered by diverse hydrologic phenomena such as groundwater inflow, prolonged moderate-intensity precipitation, or bursts of high-intensity precipitation. However, hazard assessments typically rely on simplistic hydrologic models that disregard this diversity. We used the USGS debris-flow flume to conduct controlled, field-scale slope failure experiments designed to investigate the effects of diverse hydrologic pathways, as well as the effects of 3D landslide geometries and suction stresses in unsaturated soil. Using overhead sprinklers or groundwater injectors on the flume bed, we induced failures in 6 m3 (0.65-m thick and 2-m wide) prisms of loamy sand on a 31° slope. We used 50 sensors to monitor soil deformation, variably saturated pore pressures, and moisture changes. We also determined shear strength, hydraulic conductivity, and unsaturated moisture retention characteristics from ancillary tests. The three hydrologic scenarios noted above led to different behaviors. Groundwater injection and prolonged infiltration created differing soil moisture patterns. Intense sprinkling bursts caused rapid failure without development of widespread positive pore pressures. We simulated these observed differences numerically by coupling 2D variably saturated groundwater flow modeling and 3D limit-equilibrium analysis. We also simulated the time evolution of changes in factors of safety, and quantified the mechanical effects of 3D geometry and unsaturated soil suction on stability. When much of the soil became relatively wet, effects of 3D geometry and soil suction produced slight increases ( 10-20%) in factors of safety. Suction effects were more pronounced with drier soils. Our results indicate that simplistic models cannot consistently predict the timing of slope failure, and that high frequency monitoring (with sampling periods < 60 s) is needed to measure and interpret the effects of rapid hydrologic triggers.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMNH34B..03R
- Keywords:
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- 4326 Exposure;
- NATURAL HAZARDSDE: 4328 Risk;
- NATURAL HAZARDSDE: 4330 Vulnerability;
- NATURAL HAZARDSDE: 4337 Remote sensing and disasters;
- NATURAL HAZARDS