Double-structure effects on the chemo-hydro-mechanical behaviour of a compacted active clay

This work presents an insight into double-structure effects on the coupled chemo-hydro-mechanical behaviour of a compacted active clay. In the first part, selected pore size distribution curves are introduced, to highlight the influence of solute concentration on the evolution of the microstructure of compacted samples. An aggregated structure with dual-pore network is induced by compaction even at relatively high water contents. This structural arrangement is enhanced by salinisation, and has a notable influence on transient volume change behaviour – that is, the occurrence of different stages of swelling upon pore water dilution and higher volume change rates upon salinisation. A coupled chemo-hydro-mechanical model, taking into consideration double-structural features from a chemo-mechanical viewpoint, is described and then used to interpret these behavioural responses and present complementary information on local transient processes. The model is designed to identify an intra-aggregate and an inter-aggregate domain, and assigns different values of hydraulic pressure and osmotic suction to each domain. Distinct constitutive laws for both domains are formulated, and the flow of salt and water between the two domains is accounted for by a physically based mass exchange term. The model is used to simulate salt diffusion tests run in an oedometer at constant vertical stress. Parameters used in the formulation are calibrated based on separate experimental evidence, both through direct test results and through back-analyses of laboratory experiments.