Experimental data from different testing methodologies on different compacted clayey soils, with dominant bimodal pore size distribution, are presented and analysed, to\ud provide a comprehensive picture of the evolution of the aggregated fabric along hydraulic and mechanical paths. Fabric changes are analysed both from the porous network viewpoint, by means of careful mercury intrusion porosimetry investigation, and from the soil skeleton viewpoint, by quantifying swelling and shrinkage of the\ud aggregates in an environmental scanning electron microscopy study. The consequences of the aggregated fabric evolution on the water retention properties of compacted\ud soils are analysed and discussed. A new model for water retention domain is proposed, which introduces a dependence\ud of the intra-aggregate pore volume on water content.\ud The model succeeds in tracking correctly the\ud evolution of the hydraulic state of the different soils investigated along generalised hydromechanical paths.\ud The proposed approach brings to light coupling between intra-aggregate and inter-aggregate pores in the retention properties of compacted clayey soils. Dependence of the\ud air entry and the air occlusion values on swelling and shrinking of aggregates, besides void ratio, is introduced and discussed.Peer ReviewedPostprint (published version
SUMMARYA constitutive model, accounting for multiphase and multiscale coupling, is proposed for the water retention domain and the stress-strain response of compacted clayey soils. The model is based on a conceptual interpretation of the microfabric evolution of compacted soils along generalised hydromechanical paths, detected by means of mercury intrusion porosimeter tests. Multiphase coupling is provided by the mutual interaction between the mechanical and the hydraulic states. Multiscale coupling is introduced by a measure of the size of the aggregates, which influences both the retention and the stress-strain response, in the phenomenological constitutive equations. Model capabilities are verified by comparison with relevant experimental data from laboratory tests on compacted Boom clay and other selected experimental data on different compacted clayey soils.
SUMMARYWater retention in compacted clays is dominated by multi-modal pore size distribution which evolves during hydro-mechanical paths depending on water content and stress history. A description of the evolutionary fabric has been recently introduced in models for water retention, but mostly on a heuristic base. Here, a possible systematic approach to account for evolving pore size distribution is presented, and its implications in models for water retention are discussed. The approach relies on quantitative information derived from mercury intrusion porosimetry data. The information is exploited to introduce physically based evolution laws for the parameters of water retention models. These laws allow tracking simultaneously the evolution of the aggregated fabric and the consequent hydraulic state of compacted clays. The influence of clay microstructure, mechanical constraints and water content changes on the water retention properties is highlighted and quantified from experimental data on different compacted soils with different activity of the clayey fraction. The framework is discussed with reference to a widespread water retention model and validated against experimental data on a Sicilian scaly clay compacted to different dry densities and subjected to a number of hydro-mechanical paths.
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
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