Abstract: Extreme rainfall events are the major driver of landslide occurrences in mountainous and steep terrain regions around the world. Subsurface hydrology has a dominant role on the initiation of rainfall-induced landslides, since changes in the soil water content affect significantly the soil shear strength. Rainfall infiltration produces an increase of soil water potential, which is followed by a rapid drop in apparent cohesion.
Especially on steep slopes of shallow soils, this loss of shear strength can lead to failure even in unsaturated conditions before positive water pressures are developed. A physically-based distributed model, continuous in space and time, is presented in order to investigate the interactions between surface and subsurface hydrology and landslides initiation. Fundamental elements of the approach are the interdependence of shear strength and soil water potential, as well as the temporal evolution of soil water potential during the wetting and drying processes. Specifically, three-dimensional variably saturated flow conditions, including soil hydraulic hysteresis and preferential flow phenomena, are simulated for the subsurface flow, coupled with a surface runoff routine based on the kinematic wave approximation. Evapotranspiration and specific root water uptake profiles are taken into account for the continuous simulation of soil water content during storm and inter-storm periods. The geotechnical component of the model is based on a multidimensional limit equilibrium analysis, which takes into account all the basic principles of unsaturated soil mechanics. All the components of the model are verified against well established test cases chosen from the literature. The model is applied in a small catchment in Switzerland, which is historically prone to rainfall-triggered landslides. In order to assess the overall performance of the model as well as the performance gains from the introduction of the new components several model runs were conducted. Different boundary conditions derived with several soil depth mapping techniques were utilised and the effect of preferential flow, soil hydraulic hysteresis and multidimensional limit equilibrium analysis, which are the key novel characteristics of HYDROlisthisis, was thoroughly investigated.
Citation: Anagnostopoulos, G. G., Hydrological Modelling of Slope Stability, ETH-Zürich, Diss. No. 21814, doi:10.3929/ethz-a-010120512, 2014.
Thesis (12.6 MiB, 299 downloads)