Combined use of hydraulic and hydro-mechanical modelling to investigate the drained response of a clay slope to weather conditions

The slope-vegetation-atmosphere (SLVA) interaction may have a fundamental role in the onset and progression of landsliding in clayey slopes. The extent to which the weather is crucial for the slope stability depends on both the soil hydro-mechanical behaviour and the hydraulic conditions along both the ground surface and the underground boundaries, as in the case of slopes made of fine soils bearing rocky aquifers. In this context, the Fontana Monte slope in southern Italy, affected by a deep slow-moving landslide, is considered as a prototype case of weather-induced instability phenomena in which the SLVA interaction depends not only on the climatic actions at the slope top boundary, but also on the hydrogeological set-up. In the present work, the interaction of the slope with the atmosphere, affecting the overall stability of the prototype slope, has been investigated in drained conditions through the combined use of uncoupled hydraulic simulations of the seepage and their input into limit equilibrium analyses (H+LEM), and coupled hydro-mechanical (HM) numerical modelling of the slope, under steady-state conditions representative either of the dry or of wet season. The work shows how the combined use of both H+LEM and HM approaches might help to diagnose and interpret the landslide mechanism, focusing on the impact of climate on the hydraulic and stress-strain response of the slope in the long-term. The resulting prediction of the hydraulic regime and strain field mobilised in the slope, validated through field data, supports the diagnosis of the landslide predisposing and triggering factors and the phenomenological interpretation of the three-dimensional nature of the landslide mechanism.