Experimental and numerical study of a landslide in a complex geostructural context: the case of Calita (Italy)

The Calita landslide (Northern Apennines, Italy) is a large, complex phenomenon extending over approximately 0.9 km² and characterized by a roto-translational rockslide, in a flysch-dominated area, that evolves downslope into an earth slide–earthflow covering a length of approximately 2.5 km. The earthflow sector involves clay-rich soils derived from a chaotic and strongly tectonized melange partially mixed with the progressively degradated rocky head scarp. Landslides of this type are highly sensitive to hydro-mechanical perturbations, including pore water pressure increases and undrained–drained mechanisms induced by static loading. Moreover, the litho-structural setting controls deep filtration pathways, potentially promoting localized pressurization beneath the sliding surface.

This contribution presents ongoing work aimed at developing a geotechnical model of the Calita landslide and identifying its predisposing and triggering factors. Geological surveys, field instrumentation, laboratory tests have been integrated to characterize the hydro-mechanical behaviour of the landslide body. Direct shear, oedometer, triaxial and water retention tests were performed, allowing derivation of strength parameters, permeability, and pore pressure response under saturated and partially saturated conditions. Mineralogical analyses revealed the presence of gypsum and pyrite along the landslide’s shear surfaces, indicating possible chemo-mechanical weakening mechanisms and enhanced fluid–rock interaction.

GNSS, inclinometer, and piezometric monitoring delineated the spatial variability of displacement and hydraulic pressures, with piezometers recording artesian conditions in some portions of the earth slide-earthflow. DEM of differences were produced on high-resolution Digital Terrain Models obtained during the monitoring years, from 1973 to 2024, allowing to appreciate the areas where displacements occurred and the related mobilized volumes. Finally, numerical analyses were carried out using both finite element (hydro-mechanical) and limit equilibrium approaches to evaluate slope stability under different hydraulic regimes. The results provide a consistent geotechnical framework for future scenario analyses and mitigation planning.