An approach to the interpretation of the mechanical behaviour of intensely fissured clays

The paper discusses the intrinsic properties, the geological history, the natural structure and the mechanical behaviour of intensely fissured clays from Santa Croce di Magliano, a site located within the East-side border of the Apennine chain (southern Italy). The clays were originally deposited elsewhere and subsequently moved and largely deformed during the Apennine orogenesis, so that their structure appears severely disturbed and fissured. The applicability of a continuum-based approach to describe the mechanical behaviour of a Representative Element Volume (REV, hereafter) of the natural, fissured clay is experimentally investigated by analysing the clay specimen deformation upon plane strain compression by means of False Relief Stereophotogrammetry. The results of such analysis show that, despite the intense network of pre-existing fissures, the patterns of deformation – including the eventual development of shear bands within the REV of the natural clay – are similar to those observed for unfissured clays. Triaxial tests were carried out on both natural and reconstituted clay samples, and the results were compared with those recognised in the literature to be typical of unfissured clays. Based on such comparisons, the study provides a few essential elements that are useful to define a general framework for the mechanical behaviour of intensely fissured clays.