ABSTRACT
Basic concepts and options open in the formulation of governing and constitutive equations for saturated swelling clays are examined. The focus is on changes in mechanical properties of the clay materials occurring as a result of changes in salinity. A Representative Elementary Volume (REV) for saturated clay material is defined as a closed or open system, i.e. exchanging mass internally between components, or externally with its surroundings. Basic clay property changes observed in the laboratory as well as in the field are hypothesized to be related to specific elements of their chemical and mineralogical history. Three scale phenomena within REV are identified. Nano-scale phenomena of water and cation interlamellar and external adsorption, micro-scale inter-phase mass exchange, and macro-scale chemo-mechanical coupling are the three-scale representations of the same phenomena and a procedure of re-scaling is indicated. Reversible and irreversible effects of chemical changes on clay mechanical behavior may then be hypothesized through the free energy, by identifying its mechanical stress part in both phases and that due to inter-phase mass transfers or reactions.
