Geotechnical properties of an unsaturated pyroclastic soil from Roma

The paper presents the results of an experimental investigation on the mechanical behaviour of an unsaturated pyroclastic soil typical of the subsoil of Roma (Italy). In its natural state, the material is a bonded coarse - grained weak rock. The deposits of pozzolana are unsaturated in situ; this has an important practical relevance in the evaluation of the stability conditions of natural slopes and cuts. The experimental investigation consisted mainly of pressure plate tests, oedometer tests, and special isotropic and triaxial compression tests at increasing values of mean net pressures in the range 50 - 400 kPa, and at different constant levels of suction (20 - 75 kPa). The compressibility and the shear strength properties of the material are presented in some detail. Special attention is focused on defining the failure envelope at relatively low confining stress and assessing the influence of the degree of saturation on the failure conditions.