On the geology and geotechnical properties of pyroclastic flow deposits of the Colli Albani

This paper presents the results of an experimental investigation into the engineering geology properties of three pyroclastic deposits from the Colli Albani volcanic complex, typical of the subsoil of Rome (Italy). In their natural state, these materials are coarse-grained weak rocks, generally unsaturated in situ. The mechanical properties of the material are related to the geological origin of the deposits, their formation environment and mechanisms. These are also revealed by peculiar microstructural features. A technical sheet for the description and classification of these deposits is proposed in the paper. The experimental investigation consisted mainly of identification and classification tests, one-dimensional compression and direct shear tests on saturated and dry samples. Due to their nature, non standard techniques had to be developed for sample preparation and testing. The main findings on compressibility, shear strength and creep properties of the materials are presented in the paper. Special attention is given to the definition of the failure envelope at relatively low confining stress and to the assessment of the influence of saturation on shear strength parameters.