Experimental Techniques for Unsaturated Geomaterials

Delage, Pierre; Laloui, Lyesse

doi:10.1002/9781118616871.ch4

Cited by 5 publications

(6 citation statements)

References 46 publications

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“…Finally shearing of the samples was achieved in drained conditions, with a vertical strain rate of 0.0025 mm/min. This strain rate corresponds to the recommendations available in literature for similar soil texture (Delage, 2002;Gulhati & Satija, 1981) and enables to guarantee that the difference between pore water pressure and air pressure (uw-ua) remains constant during shearing. The crosssection of samples under loading was calculated according to Head & Epps (1980).…”

Section: Suction-controlled Triaxial Testssupporting

confidence: 66%

Accounting for the microstructure for the prediction of unsaturated shear strength of remolded fine-grained soils

Mpawenayo

Gérard

2024

Can. Geotech. J.

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Predictions of the unsaturated shear strength with generalized effective stress-based approaches disregard the non-uniform microstructure of remolded fine-grained soils. The study aims at investigating the adequacy of microstructurally-based effective stress to predict the unsaturated shear strength of remolded fine-grained soils over a wide range of suctions. For that purpose, shear strength data are acquired on a silty clay soil compacted at two different dry densities through suction-controlled triaxial tests and unconsolidated triaxial tests at constant water content. The microstructure of the soil at the as-compacted state is determined with Mercury Intrusion Porosimetry and is directly incorporated in different expressions of microstructurally-based effective stress available in the literature. The experimental data suggest that compared to the generalized effective stress, microstructurally-based effective stress expressions provide better predictions of the unsaturated shear strength, especially at high suctions. Also, the use of microstructurally-based effective stress is particularly relevant for remolded fine-grained soils compacted at high dry densities, i.e. with a low proportion of macropores.

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Section: Suction-controlled Triaxial Testssupporting

confidence: 66%

Accounting for the microstructure for the prediction of unsaturated shear strength of remolded fine-grained soils

Mpawenayo

Gérard

2024

Can. Geotech. J.

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“…In macro-scale experiments, to relate cohesion, or strength in general, to suction, it is customary to first bring an originally unloaded sample to a desired level of saturation, and then at a constant saturation, load the material until yielding (see e.g. Delage, 2013). At micro-scale, however, the attractive adhesion force has its maximum at a close contact of the grains (almost, but not necessarily, at zero separation) and decreases during an increasing separation, lowering the strength of adhesion, as seen in experiments with evaporation and extension of two-grain systems (Mielniczuk et al, 2014a).…”

Section: Micro-scale Experimentsmentioning

confidence: 99%

Adhesion-force micro-scale study of desiccating granular material

2020

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Experiments on five-, four-, three-and two-wet-hydrophilic-grain clusters were performed to investigate evolution of adhesion of granular media during drying on the micro-scale. The experiments show that the adhesion-force of a cluster initially grows at most to three times the original value before decreasing to zero by the end of evaporation. The adhesion-force is composed of capillary pressure force acting over the liquid/solid contact surface area, and surface tension forces acting over the three-phase contact perimeter length. This is in contrast with most macro-scale phenomenological models, in which the only desaturation process variables affecting strength are suction and saturation. Both the contact surface area and contact perimeter length are reduced to zero upon complete liquid evaporation. The morphology of an evaporating water body evolves through slow flow controlled by evaporation rate, interrupted by various modes of fast air entry, which are non-equilibrium jumps of liquid/gas interfaces (Haines jumps). The instabilities involve large adhesion force discontinuities and substantial water mass reconfiguration with water flow in an extremely short time, which makes the process transient. The reconfigurations can reduce the original multi-grain water clusters to four-, three-and two-grain clusters by way of three different instability modes: of thin-sheet instability, or meniscus snap-through instability, depending on the sign of the Gauss curvature of the liquid surface, or finally, for two-grain bridges only, a liquid wire pinch-off. For larger meso-scale assemblies, however, the global adhesionforce evolution is little affected by the jumps. The air entries are potential sites for drying cracks. The (approximately) calculated capillary pressure for two-and three-grain clusters, in no cases is seen to reach high values, predicted from water retention curves.

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“…Because of the multiscale structure of clay minerals, a continuum of water populations, usually divided into interparticle and interlayer water, is observed when smectites are exposed to water vapor, Figure . − The interlayer water can be further separated into water that directly hydrates the interlayer cation (termed cation-coordinated water herein), H-bonded water that surrounds the cation-coordinated water, and water that is loosely H-bonded to the clay mineral surface. Some of the interlayer water can be strongly bound, having suction potentials well in excess of several tens to hundreds of MPa . The intraparticle water includes water found at the edges and external surfaces of the layer structure and some of this may indeed act as weakly H-bonded interlayer water.…”

Section: Introductionmentioning

confidence: 99%

“…Simplistic model of the water population continuum in Ca-Mt usually divided into interparticle (water residing within pores) and interlayer (cation-coordinated water that is retained to very high suction potentials, tightly H-bonded water that hydrates the cation-coordinated water and water that is weakly H-bonded to the clay mineral surface) water . The energy of H-bonded water decreases from cation-coordinated to tightly H-bonded to weakly H-bonded interlayer water to bulklike intra- and interparticle water.…”

Section: Introductionmentioning

confidence: 99%

Electric Field Induced Polarization Effects Measured by in Situ Neutron Spectroscopy

et al. 2017

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Despite the success of electrical stimulation in many areas, including clay or sludge dewatering, extraction of juices from fruit pulp, fracture healing, and targeted drug delivery, the induced transport mechanisms are controlled by unknown factors. While electroosmotic dewatering of clays particles <10 μm is well-known, understanding of how tightly bound water molecules are removed from within the clay interlayers is still incomplete. By performing quasielastic neutron scattering experiments with in situ electric field stimuli on calcium montmorillonite (Ca-Mt) prehydrated at relative humidity (RH) of 58 and 85%, we observed an increase in the water mean residence time, suggesting that hydrogen bonding lifetimes are prolonged under electric field. Assuming that at these RH most all water present resides within the interlayer space of the Ca-Mt, this result indicates strong polarization of the water by the interlayer cation. This electroosmotic induced reorganization has important implications in terms of ion mobility and aqueous chemical reaction mechanisms.

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Experimental Techniques for Unsaturated Geomaterials

Cited by 5 publications

References 46 publications

Accounting for the microstructure for the prediction of unsaturated shear strength of remolded fine-grained soils

Accounting for the microstructure for the prediction of unsaturated shear strength of remolded fine-grained soils

Adhesion-force micro-scale study of desiccating granular material

Electric Field Induced Polarization Effects Measured by in Situ Neutron Spectroscopy

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