Spatially distributed modeling of landslide triggering: An approach based on principles of unsaturated soil plasticity

This paper discusses an analytical approach to define Factors of Safety (FS) for shallow slopes based on plasticity theories for unsaturated soils. The objective is to use such indices in landslide susceptibility analyses at the regional scale, thus gaining a mechanistic interpretation of the variability of the failure mode, as well as of the role of the evolving hydrologic state. For this purpose, two mechanisms of failure have been considered: uncoupled mechanisms due to drained frictional failure (here referred to as soil slips) and fully coupled mechanisms associated with an unstable pressurization of the pore fluid (here referred to as flowslides). For each scenario, expressions of FS have been derived in analytical form by identifying losses of uniqueness and/or existence of the deformation/wetting response predicted by a simple model for unsaturated sloping ground. To test the hypotheses, a dataset of landslides occurred in Southern Italy in 1998 has been used. For this purpose, the FS values have been combined with a hydrologic model to simulate pore pressure transients due to rain infiltration, thus enabling an integrated assessment of the spatially-distributed patterns of frictional slips and flow failures at regional scale. Preliminary results show the possibility to capture some of the main morphometric characteristics of these events, such as the overall distribution of types of failure with respect to slope angle and/or failure depth, suggesting that principles of unsaturated soil plasticity represent convenient tools to augment physicallybased models for landslide forecasting.