The geo-hydro-mechanical properties of a turbiditic formation as internal factors of slope failure processes

Similar to many inner areas of Southern Europe, the Daunia Apennines are affected by widespread landsliding, often consisting of slow, deep-seated movements. Recurrent acceleration of these landslides causes damage to buildings and infrastructures, severely biasing the socio-economic development of the region. Most landslides in the area of study occur within clayey units of turbiditic flysch formations, often severely disturbed by tectonic thrust and previous landsliding. The Faeto Flysch (FAE) is one of the most widespread turbiditic formations in the Daunia Apennines and is representative of the tectonised geological formations involved in slope failure. This work, by examining the landslide processes occurring at four pilot sites, aims at connecting the observed mechanisms to the geo-hydro-mechanical setup of FAE in the slopes. It is found that the soil portion of FAE consists of highly plastic clays, resulting in low intrinsic shear strength, and hence controls the initiation and progression of failure in the slopes, as such representing an internal predisposing factor to landsliding. In addition, the presence of fractured rock strata confers a high permeability at the slope scale, with respect to that of the soil matrix. This results in severe piezometric levels in the slope, which represent another internal predisposing factor to failure, and in the ability to induce significant seasonal pore water pressure oscillations down to great depths, connected to rainfall infiltration, thus triggering the recurrent acceleration of the landslides.