Influence of hydraulic properties on physically modelling slope stability and the definition of rainfall thresholds for shallow landslides

Abstract

Physically-based models are recognized as a good tool for slope stability analysis and have been implemented for the definition of rainfall thresholds for landslides. In this study, a methodology for estimating rainfall intensity and duration thresholds for shallow sliding failure, using the physical model TRIGRS, was implemented in a tropical mountainous basin of the Valle de Aburrá (Colombia). The variation of pressure head and factor of safety during different rainfall events and hydraulic conditions is studied for specific grid cells. Steady state and a maximum pressure head were reached for each grid cell regardless of the different rainfall intensities and hydraulic conductivities simulated, but the time in which this condition is reached depends on these variables and occurs faster for steeper slopes. The influence of hydraulic properties on the stability results and the position of the rainfall intensity and duration thresholds were studied with parametric analysis. Very low values of saturated hydraulic conductivity do not allow rainfall intensity and duration thresholds to be developed. The rainfall threshold position also has a greater variation with respect to the parameters of the soil water retention curve and the initial infiltration rate (or long-term background rainfall rate) for low values of saturated hydraulic conductivity.