Collaborative Research: Multi-Dimensional and Multi-Physics Analysis of Rainfall-Induced Landslides and Runout

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Landslides are continual natural hazards that can damage infrastructure and cause significant loss of life as occurred in the Oso Landslide (March 22, 2014) in Snohomish County, Washington. Some landslides are rapid and exhibit large runout over few minutes, whereas others are intermittent and move only small distances in a given year. Both of these hazards are usually triggered by precipitation. The main objective of this research project is to develop a three-dimensional (3D) slope stability framework that incorporates unsaturated soil hydraulic properties, effective stresses, and shear strengths to better predict the location, shape, and depth of rainfall-induced landslides, such as the recent Oso Landslide near Seattle and the La Conchita Landslides (1995 and 2005) near Los Angeles. The proposed 3D model will be used to simulate time-dependent variations in saturation from water infiltration, impact of surface vegetation and timbering, and rises in hydrostatic pore-water pressures from runoff that will be used to predict the runout distance based on the calculated factor of safety, slope angle, and pore-water pressures after triggering. The key product of this research will be a new validated framework for slope stability analyses and landslide risk assessment. This 3D variably-saturated stability analysis framework is important because it accounts for the following factors that are not incorporated in traditional two-dimensional (2D) limit equilibrium slope stability analyses: (1) effective stresses under both saturated and unsaturated conditions, (2) stress-dependent unsaturated and saturated strength envelopes, (3) 3D slide mass geometry, volume, shear forces, and boundary conditions, (4) spatial variation and depth of the unsaturated zone and hydrostatic pore-water pressures across the slide mass, and (5) variation in unsaturated and saturated soil shear strength across the slide mass. Current limitations with 2D analyses affect the calculated limit equilibrium factor of safety and thus the ability to predict the occurrence, shape, volume, and runout distance of the potential slide mass. For example, a 2D analysis does not provide an estimate of the 3D shape and volume, which is key to predicting slide mass volume, pore-water pressures, and runout distance. The results of this project will improve landslide detection, prediction, hazard mapping, land-use planning, and property rights policy decisions. For new subdivisions the geotechnical concerns can be identified and zoning adjusted to manage the risk with the proposed 3D analysis.