Pedological discontinuities as potential factors of shallow landslides

This research work is part of a wider research project (PONOl-01503: "Integrated systems for hydrogeological risk monitoring, early warning and mitigation along the main lifelines"), aimed at hydro-geological risk mitigation and early warning along three highway sections of southern Italy. In particular, the main results summarized here are focused on the assessment of shallow landslide susceptibility along the A3 highway section between Cosenza Sud and Altilia in northern Calabria. A detailed geological and geomorphological survey allowed us to map the main lithological, structural and relief features of the landscape, with a special emphasis on active, dormant and inactive landslides and their gee-lithological control factors. A soil survey was also carried out in the field, showing a domina nee of Entisols and Inceptisols on steep slopes, and Mollisols and Alfisols on gentle landforms. Soil observations were focused on the identification of pedological discontinuities as potential factors that might trigger shallow landslides. A number of soil profiles, often close to landslide scarps, evidenced significant morphological changes of the parent materials, such as texture, pedogenic structure, dry consistence and moisture, or hydromorphic features caused by transient water-logging conditions, and clay-illuviated horizons. Buried soils were recognized, often truncated by erosion, and overlain by younger soils developed on colluvia, debris flows and detrital slope deposits. Five representative soil profiles were selected and sampled for both pedological and geotechnical laboratory analyses. Bulk and undisturbed samples were collected, (i) for chemical and physical soil analyses (particle size distribution, organic and inorganic carbon, pH, electrical conductivity, soluble salts), and (ii) for determining bulk density, Atterberg limits, cohesive strength, angle of internal friction, water retention and for thin sections to be observed under an optical polarizing microscope, respectively. Preliminary results of laboratory analyses showed irregular patterns of both pedological and geotechnical data along the soil profiles, coherently with field observations.