On Unsaturated Soil Mechanics – Personal Views on Current Research

Pande, G. N.; Pietruszczak, S.

doi:10.1515/sgem-2015-0035

“…At degrees of saturation below the residual degree of saturation (i.e. < S r,res =0.09), water phase became discontinuous (Fredlund et al 1993;Pande and Pietruszczak 2015;, thus the flow of liquid water stopped and the matric suction equalisation was driven by the flow of water vapour only and therefore, t se approached zero as evident in Fig. 10.…”

Section: R a F Tmentioning

confidence: 93%

Impacts of matric suction equalization on small strain shear modulus of soils during air drying

Ngoc

¹

,

Fatahi

²

,

Khabbaz

³

et al. 2020

Can. Geotech. J.

2

0

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In this study, a weight-control bender element system has been developed to investigate the impact of matric suction equalisation on the measurement of small strain shear modulus (Gmax), during an air-drying process. The setup employed is capable of measuring the shear wave velocity and the corresponding Gmax of the soil sample in either an open system in which the soil sample evaporates freely or in a closed system that allows the process of matric suction equalisation. The comparison between measurements of Gmax in the open and closed systems revealed underestimations of Gmax when matric suction equalisation was ignored due to the non-uniform distribution of water content across the sample cross-sectional area. This study also investigated the time required for matric suction equalisation tse to be established for samples with different sizes. The experimental results indicated two main mechanisms, driving the matric suction equalisation in a closed system during an air-drying process, namely the hydraulic flow of water and the flow of vapour. While the former played the key role when the micro-pores were still saturated at the high range of water content, effects of the latter increased and finally dominated when more air invaded the micro-pores at lower water contents.

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“…Recent measurements of the refractive index of bovine α-crystallin solutions that were prepared in the same manner as that for the data analyzed here, 11 and analyzed with use of the same UV extinction coefficient, found ∂n/∂c α = 0.165 ± 0.005 cm 3 /g. 59 These available measurements were taken for the respective pure protein solutions, and we do not have data for the index of refraction, n, over the entire concentration and composition range for which light scattering efficiency data were obtained. Therefore, we adopt a model for the index of refraction of the mixtures, by using the measurements of the refractive index increments of γB-and α-crystallin just stated to construct a model for the optical-frequency polarizability of their concentrated mixtures.…”

Section: B Refractive Index Modelmentioning

confidence: 99%

“…On the other hand, the calculations to be presented below do give some insight into the origins of the low-concentration, concave-down dependence of the scattered intensity on the relative proportions of α and γ-crystallin, as we describe below in connection with Eq. (59).…”

Section: Scattering From Dilute Mixtures: Virial Coefficientsmentioning

confidence: 99%

Statistical-thermodynamic model for light scattering from eye lens protein mixtures

Bell

¹

,

Ross

²

,

Bautista

³

et al. 2017

The Journal of Chemical Physics

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We model light-scattering cross sections of concentrated aqueous mixtures of the bovine eye lens proteins γB-and α-crystallin by adapting a statistical-thermodynamic model of mixtures of spheres with short-range attractions. The model reproduces measured static light scattering cross sections, or Rayleigh ratios, of γB-α mixtures from dilute concentrations where light scattering intensity depends on molecular weights and virial coefficients, to realistically high concentration protein mixtures like those of the lens. The model relates γB-γB and γB-α attraction strengths and the γB-α size ratio to the free energy curvatures that set light scattering efficiency in tandem with protein refractive index increments. The model includes (i) hard-sphere α-α interactions, which create short-range order and transparency at high protein concentrations, (ii) short-range attractive plus hard-core γ-γ interactions, which produce intense light scattering and liquid-liquid phase separation in aqueous γ-crystallin solutions, and (iii) short-range attractive plus hard-core γ-α interactions, which strongly influence highly non-additive light scattering and phase separation in concentrated γ-α mixtures. The model reveals a new lens transparency mechanism, that prominent equilibrium composition fluctuations can be perpendicular to the refractive index gradient. The model reproduces the concave-up dependence of the Rayleigh ratio on α/γ composition at high concentrations, its concave-down nature at intermediate concentrations, non-monotonic dependence of light scattering on γ-α attraction strength, and more intricate, temperature-dependent features. We analytically compute the mixed virial series for light scattering efficiency through third order for the sticky-sphere mixture, and find that the full model represents the available light scattering data at concentrations several times those where the second and third mixed virial contributions fail. The model indicates that increased γ-γ attraction can raise γ-α mixture light scattering far more than it does for solutions of γ-crystallin alone, and can produce marked turbidity tens of degrees celsius above liquid-liquid separation. Published by AIP Publishing.

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“…• 0 S\S C isolated water regions or lenses (pendular regime) • S C \S\S B interconnected water and air (funicular regime) • S B \S 1 isolated air bubbles with the bounds S C % 0:2 and S B % 0:8 being tentative estimates, see [8] and Sect. 6 for microstructural considerations.…”

Section: Introductionmentioning

confidence: 99%

Bishop parameter $$\chi $$ from static equilibrium

Niemunis

¹

2022

Acta Geotech.

0

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For unsaturated soils, Terzaghi’s effective stress $$\sigma = \sigma ^\mathrm{tot}- u$$ σ = σ tot - u has been generalized by Bishop to the form $$\sigma ^B = \sigma ^\mathrm{tot}- \chi u$$ σ B = σ tot - χ u . Factor $$\chi $$ χ , for example $$\chi (S) \approx S$$ χ ( S ) ≈ S , takes into account the degree of saturation S. However, $$\sigma ^B$$ σ B is unable to characterize strength and deformation of soil unless applied with suction. A new stress $$\sigma ^E = \sigma ^\mathrm{tot}- \chi ^E u$$ σ E = σ tot - χ E u with $$ \chi ^E(S,n) $$ χ E ( S , n ) is proposed. It is likewise insufficient if applied without suction, but it has (at least) a clear physical meaning: $$\sigma ^E$$ σ E represents contact forces between grains in the static equilibrium in the same manner as the effective stress does in saturated soils. All grains must be entirely surrounded by free or capillary water.

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On Unsaturated Soil Mechanics – Personal Views on Current Research

Cited by 12 publications

References 44 publications

Impacts of matric suction equalization on small strain shear modulus of soils during air drying

Impacts of matric suction equalization on small strain shear modulus of soils during air drying

Statistical-thermodynamic model for light scattering from eye lens protein mixtures

Bishop parameter $$\chi $$ from static equilibrium

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