CESS Seminar: Experimental assessment of the fabric and state parameters of active clays for modelling their hydro-chemo-mechanical behaviour
Abstract. The osmotic, hydraulic and self-healing efficiency of bentonite based barriers (e.g. geosynthetic clay liners) for containment of polluting solutes are governed both by the physico-chemical intrinsic parameters of the bentonite, i.e. the solid phase density (ρsk), the total specific surface (S), and the total fixed negative electric surface charge (s), and by the state and fabric parameters able to quantify the soil density and microstructure, i.e. the total (e) and nano (en) void ratio, the average number of platelets per tactoid (Nl,AV), the effective electric fixed-charge concentration (), and the Stern fraction (fStern). In turn, the fabric parameters seem to be controlled by the effective stress history, ionic valence and related exposure sequence of salt concentrations in the pore solution. A theoretical framework, able to describe the coupled chemical, hydraulic and mechanical behaviour of bentonites, has been set up. In particular, the relationships, which link the aforementioned intrinsic, state and fabric parameters of a given bentonite with its hydraulic conductivity (k), effective diffusion coefficient (), osmotic coefficient (w) and swelling pressure (usw) under different stress-histories and solute concentration sequences, are presented. The proposed theoretical framework has been validated through the comparison of its predictions with some of the available experimental results that have been obtained through the use of the last version of an ad hoc equipment able to detect, within a unique time step, all the aforementioned performance parameters, apart the hydraulic conductivity (k) that has been anyway measured by just a further time step carried out always with the same equipment and on the same bentonite sample.