A Physically-based 3D Landslide Susceptibility Model for Shallow Translational Landslides using DEM

Shallow landslides are frequently observed at natural slopes and often lead to more destruction through flow-like disasters. Traditionally, physically-based landslide susceptibility models utilized infinite slope stability analysis to determine slope stability in terms of factor of safety (FS) over regional scales. Although the infinite slope model is computationally less demanding, it cannot account for the spatial variability of soil properties and the three-dimensional (3D) effects arising from complex topography. However, using 3D slope stability models is computationally demanding and suffers from discontinuity introduced by abrupt changes in soil thickness. Therefore, this research proposes a new Three-Dimensional Translational Shallow (3DTS) slope stability model to overcome these drawbacks of the existing models with complex 3D sliding surfaces.

The developed 3DTS model utilizes the Green-Ampt (GA) infiltration model and the 3D extension of the Janbu simplified method of slope stability. The 3DTS utilizes a generalized GA model to account for non-uniform infiltration history and compute the surface runoff. In 3D limit equilibrium slope models, the failing soil mass must be subdivided into rigid soil columns; however, the developed 3DTS uses the cells from a digital elevation model (DEM) as the rigid soil columns. The shear strength, modeled with the Mohr-Coulomb criterion, is provided by the soil frictional resistance on the base and the side regions of the outermost soil columns. Additional strength from the vegetation roots at the shallow surfaces is modeled.

The method used in the developed 3DTS model for generating slip surfaces from DEM cells was verified by comparing computed FS with the 3-Dimensional Probabilistic Landslide Susceptibility (3DPLS) model, which uses ellipsoidal slip surfaces. A parametric study analyzed the sensitivity of the slip surface's shape, the side soil resistance, and the vegetation resistance to shallow translational failures. The applicability and computational efficiency of the developed 3DTS for large-scale landslide susceptibility assessment were demonstrated by analyzing landslide case studies in Norway and South Korea.

This work is the result of collaboration between Norwegian Geotechnical Institute (NGI) and Korea Advanced Institute of Science and Technology (KAIST) through the project GEOMME (2021-2026; Pnr. 322469), “Climate-induced geohazards mitigation, management, and education in Japan, South Korea, and Norway”, supported by the Research Council of Norway.