Slope stability and groundwater flow system in the area of Lizzano in Belvedere (Northern Apennines, Italy)

In Northern Apennines, landslides involving weak rocks such as clay shales are widespread and often cause damage to public infrastructure and private properties. These landslides, mostly classifiable as earthflows, generally exhibit continuous slow movements, with temporary increases of velocity controlled both by groundwater and rainfall regime. Although the relationship between precipitation, groundwater flow and displacement rate is evident, its quantitative description remains problematic. We use piezometric and slope movement continuous monitoring to investigate the groundwater flow system in the vicinity of the contact between clay shales and overlying more permeable units, where the village of Lizzano in Belvedere is located. Our aim is to describe the groundwater flow and its relation to slope deformation in order to simulate the effect of possible drainage measures both on piezometric levels and expected displacement rates. Timing and magnitude of piezometric responses at different depths are related to observed deformations and used to calibrate a transient 3D groundwater flow model. Groundwater modeling validates the conceptual hydrogeological scheme and allows simulation of the impact of surface and deep drainages on piezometric levels. Results indicate that horizontal drains are more effective than infiltration reduction measures, both in terms of drawdown and time effectiveness of action. Simulated hydraulic heads are then used to produce a probabilistic prediction of the expected displacement rates by means of an empirical method. In the case of Lizzano in Belvedere, according to our results, the lowering of hydraulic heads operated by horizontal drains can reduce the velocity of slope movements from centimeters per year to millimeters per year.