Mechanical behaviour of Palermo and Marsala calcarenites (Sicily), Italy

This paper aims at finding a framework for the Sicilian Calcarenites relating the strength and the deformability of these materials to their geological and structural features: fabric, bonding, initial and actual specific volume. In particular, this study sets out to separate the effects of fabric and of bonding on the mechanical response. The investigated lithotypes, Calcarenites from Palermo and Marsala, outcropping in many areas of southwestern Sicily, are characterized by sudden changes in their deformability, strength and permeability characteristics. The geotechnical identification, by means of computerized axial tomography and thin section petrographic analysis suggested a subdivision of these two calcarenites into five lithotypes as a function of their structural configuration. These calcarenites are metastable rocks whose mechanical behaviour depends on the fabric and bonding. Oedometer, triaxial and isotropic tests were conducted to analyzed interparticle bonding and/or fabric effects on the mechanical behaviours. For each lithotype the yield limit was defined and three distinct behavioural patterns were identified as a function of the confining stress level: 1) an initial linear elastic behaviour up to the yielding strength, 2) a yielding phase characterized by a strain-softening response, 3) a final phase of the destructured material. At yield state, bonding is the major factor contributing to the soil strength, while the effect of fabric comes into play at post-yield stress state. For the assessment of the yielding conditions the yield stress values obtained from various stress-paths were taken into account.