Groundwater modelling of a weathered gneissic cover

Knowledge of the groundwater regime, which is generally necessary in studying the stability of slopes, is of fundamental importance in the analysis of landslide involving intensely weathered rocks, as in the case of a landslide in the western Sila Massif (southern Italy)reactivated by heavy and prolonged rainfall. For this landslide, the total absence of displacements during the actual quiescence period of the critical rainfall events did not allow measurements of the critical pore pressures capable of reactivating the landslide. To solve such a problem, a saturated-unsaturated flow model was calibrated taking into account in situ pore pressure measurements acquired over a long period of time. The analyses permitted determination of the role played by the hydraulic heterogeneity of the involved soils and the hydraulic boundary conditions for simulations of the response of in situ pore pressures to rainfall. Such conditions were therefore used to predict the critical unknown values attained during landslide reactivations and were indirectly tested using different methods.