Rainfall thresholds for shallow landslides based on a numerical analysis

Shallow landslides in Alpine regions frequently occur during heavy precipitation events or extremely fast snow melting processes. Early-warning is mostly based on simple empirical rainfall intensity and duration curves indicating probable critical climatic conditions for slope stability. However, the occurrence of weather-induced landslides depends not only on the immediate action of rain and snow melt, but also on different predisposition factors. An example of application of numerical analyses for the establishment of rainfall thresholds is presented. A coupled hydro-mechanical formulation is used in order to analyse the triggering of shallow landslides in initially partially saturated slopes induced by different rainfall patterns. The numerical simulations on soil slopes for which the soil parameters have been calibrated from field and laboratory measurements enable associating different failure mechanisms to the observed failures in the field.