Numerical modelling of the motion of rapid, flow-like landslides for hazard assessment

Abstract

Computer methods for analysis of stresses, strains and displacements of soil structures have made spectacular advances in recent years. Now, a new field of analysis with substantial practical significance is opening up. This is the quantitative analysis of motion of rapidly moving masses of earth and fragmented rock in landslides such as debris avalanches, debris flows, flow slides and rock avalanches. The new methods accept an unstable body of material on the slope as input (the “landslide source”) and map its propagation down the slope in terms of flow depth and velocity. This allows outlining the extent of potential hazard areas and the distribution of hazard intensity parameters within them as needed for detailed hazard mapping, estimation of risks and design of remedial measures such as deflecting walls, dykes or barriers. Two advanced numerical solutions based on integrated “shallow-flow” Lagrangian theory of unsteady flow of non-Newtonian fluid are described in terms of their theoretical background, assumptions regarding the type of flow and rheological characteristics, as well as examples of a variety of results. The two models are the pseudo-three dimensional code DAN and its extension into three dimensions, DAN3D. Both codes have the following main capabilities: 1) Open rheological kernel, allowing the choice of a variety of rheological relationships to suit a particular character of the moving mass; 2) ability to change rheology during the flow; 3) non-hydrostatic, anisotropic internal stress distribution controlled by longitudinal strain; and 4) ability to entrain material during the flow. Both codes are highly efficient and both produce similar results when applied to the same example.