Geotechnical and landslide aspects in weathered granitoid rock masses (Serre Massif, southern Calabria, Italy)

The weathering processes produce important chemical and physical transformations in rock masses producing adecay of their strength and then stability. In this study different methodologies were employed to define thephysical-mechanical properties and the minero-petrographical changes at each grade of weathering, useful todetermine a geological model of the weathered granitoids involved in mass movements. The paper focuses ona multidisciplinary research on the weathering profiles of the Paleozoic granitoid rocks surrounding the villageof Fabrizia located in the SerreMassif (southern Calabria, Italy). Fabrizia lies on an old erosion surface composedof basement rocks made up of weathered granitoids, belonging to the Serre Massif granitoid complex, and overlainby thin eluvial-colluvial deposits.The tectonic uplift of the area combined with Mediterranean climatic conditions, both active at least since theQuaternary, are the main causes of the deepweathering of the plutonic rocks. Theweathered profiles of the granitoidcomplex have been studied through field observations, borehole explorations with geotechnical tests andseismic surveys coupled to minero-petrographical analysis and laboratory tests. Weathered profiles are mainlycomposed by rock masses varying from completely weathered and residual soil (classes V–VI) to moderatelyweathered rocks (class III), characterized by a progressive increase of geotechnical properties (e.g., seismicwave velocity, rock quality designation, internal friction angle, uniaxial compressive strength) with a decreaseof weathering. The weathered rocks display a wide variety of mass movement. Landslide types are rockfalls forthe fresher rocks (class III); translational slides occur between different weathering degrees (classes IV and V)and rotational slides dominate at the top of the slopes and generally involve the weathering grades from classIV to classes V–VI. The shallow horizons are composed of thin eluvial-colluvial deposits and more weatheredgranitoids (classes V–VI) that may generate dangerous debris flows or debris avalanches during intense andprolonged rainfall. The landslide surface is usually at a depth lower than 2min the debris flowtype,while deeperlandslides (depth N 2 m) are rotational and translational typeswith sliding surfaces occurring mainly in the transitionbetween the classes IV and V.The field survey coupled to geotechnical, geophysical and minero-petrographical data allowed the recognition ofthe different weathered horizons and relative geotechnical properties useful to the reconstruction of the reliablegeological model. The model represents an important support for the study of the landslide processes and for asustainable management of the territory. The used approach provided results to set a general reference frameworkfor establishing more precise correlations betweenmassmovement phenomena and weathering processes

Granitoid rocksWeathering profilesGeotechnical parametersLandslidesSouthern CalabriaItaly