FRANE TIPIZZATE IN ROCCE GNEISSICHE: RILEVANZA E STATO DELL'ARTE

The analysis of landslide, essential for designing remedial works in risk management, presents considerable complexities, requires a significant commitment and is time consuming. The systematic analysis of the results concerning studies of representative landslides in homogeneous geonvironmental and social contexts allows to identify ?families? of typified landslides intended here as two or more landslides that have similar charac- teristic elements (geomaterials, maximum depth, velocity, etc.). This paper proposes a method able to both define landslide mechanisms linked to a family of typified landslides and export the knowledge from a single slope to large area and regional analyses in a circular and effective way. The spread of high-grade metamorphic rocks in the Calabria Region, especially gneissic ones, and their deeply weathering conditions expose them to a high landslide occurrence. In this context, the proposed method and the related results are useful tools for defining effective strategies for adaptation, mitigation and reduction of landslide risk. The Calabria territory represents a "landslides laboratory" in which the performed studies and the obtained results allowed to gather a big amount of data that can be analysed by the proposed method. In the paper, regional level of analysis, that use the map of weathering and the landslide inventory map (PAI), allows to typify the relationship between three macro classes of weathering (macro-class A, loose rock; macro-class B, weak rock; and macro-class C, hard rock) and landslides. At large area level, the paper focuses on two study areas affected by shallow (deep of the sliding surface less than 3 m), medium-deep (up to 30 m deep) and deep-seated landslides (deeper than 30 m) involving deeply weathered gneissic rocks. Weathering profiles are generally complex and the geometric relationships between weathering classes (i.e., class VI - residual and colluvial soils; class V - completely weathered rock; class IV - highly weathered rock; class III - moderately weathered rock; class II - slightly weathered rock; and class I - fresh rock) can be transitional (i.e., 'canonical' or 'normal/regular' sequence) or abrupt when controlled by joints/faults or rock structure (due to the compositional heterogeneity of the gneiss). The performed analyses allow to typify landslides in terms of weathering classes, prevalent kinematic characteristics, maximum depth of the sliding surfaces. Single slope level of analysis, using of the available detailed geological, lithotechnical, geomorphological and geotechnical re- sults, allows identifying, from studies directly finalized to the definition of the geological and the geotechnical models of two landslides (medium deep and a deep seated), further specific elements that concur to typify the landslides affecting weathered gneissic rocks. The obtained results, which must be confirmed, indicate the usefulness of the approach. In particular, regional level of analysis allows identifying the areas to be analysed at large area level. The typified elements defined from large area level of analysis allow the selection of other more widespread and representative landslides to be analysed at slope level with field surveys, geotechnical investigations, monitoring, modelling, etc. The same typified elements allow to plan the priorities of the remedial works and to better define the use of the available resources. Finally, slope level of analysis allows maximizing the knowledge acquired for assigned resources and, therefore, to guarantee in the medium-long term greater socio-economic sustainability of the realised remedial works.