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

Abstract

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

Shear displacements induced by decrease in pore solution concentration on a pre-existing slip surface

“…Many authors discussed the possibility that pore water pressure may change during the process of exposure to a fluid different from the pore fluid, as an effect of osmotic processes at the specimen scale (Mitchell et al, 1973;Barbour and Fredlund, 1989;Gajo and Loret, 2004;Musso et al, 2013), as well as an effect of the diffusion of high concentration ionic front (Santamarina and Fam, 1995).…”

Microstructural changes of an undisturbed, reconstituted and compacted high plasticity clay subjected to wetting and drying

“…The pore size density (PSD) functions, for both saturated and unsaturated soils, obtained from mercury intrusion porosimetry (MIP) have been shown to evolve as a result of hydraulic, mechanical and chemical changes (Delage and Lefebvre, 1984;Delage et al, 1996;Romero et al, 1999;Simms and Yanful, 2001;Koliji et al, 2006;Casini et al, 2012;Musso et al, 2013;Wang et al, 2013). Despite this, there is still limited understanding of how the soil microstructure evolves during combined hydraulic and mechanical paths.…”

Microstructural effects of environmental salinity on unbound granular road pavement material upon drying

“…Therefore, any microstructural changes can be attributed to the salt crystallization rather than to any osmotic effects as sometimes observed on compacted soils [3,11]. It can be observed that the maximum mercury intrusion void ratio (e MIP ) of the specimens tends to decrease with increasing concentrations (Fig.…”

“…Moisture and soluble salts it contains migrate upwards under suction gradients due to evaporation and, close to the road pavement surface, the salts tend to accumulate in a crystalline form, which can result in significant damage to thin bituminous surfacings [12][13][14] because of the increase in volume associated with salt precipitation. Although some studies examined the microstructural changes in compacted soils subjected to salinization [3,11], very few of them looked at the microstructural effects associated with naturally occurring salt crystallization on granular road pavement materials. In particular, little effort was made to quantify the microstructural changes in terms of pore size distribution (inferred from mercury intrusion porosimetry), despite the fact that understanding microscale phenomena often helps explaining macroscopic behaviors [6,16].…”