Structure, properties and mechanical behaviour of the highly plastic intensely fissured Bisaccia clay shale

The Apennines chain, in Italy, is constituted by a sequence of thrust sheets, including clay shales of marine origin, whose structural features are strictly related to the complex stress field induced by orogenesis and by subsequent geological processes. Large outcrops constituted by tec- tonized clay shales are characterised by an intensely fissured fabric induced by intense shearing caused by tectonism. Such a fabric governs soil properties and mechanical behaviour, sometimes obscuring the influence of index and state properties. However, these latter as well as some bonding, can play an important role, depending on concerned geotechnical problems and induced stress paths. The paper deals with a typical tectonised formation, the highly plastic Bisaccia Clay Shale, focusing the relationship among mentioned factors, which are related to both depositional and epigenetic processes, and hydraulic and mechanical properties. The remarkable role of the pore liquid on the prop-erties of such a highly plastic material is also discussed. In particular, laboratory data give some insight on the mechanisms of softening and on its role on soil behaviour