Modeling Hydraulic Conductivity and Swelling Pressure of Several Compacted Bentonites Affected by Salinity of Water

Tanaka, Yukihisa; Hasegawa, Takuma; Nakamura, Kiyoji

doi:10.2208/jscejc.65.66

Cited by 6 publications

(4 citation statements)

References 12 publications

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“…Effects of exchangeable cations and/or dry density on the hydraulic conductivity of bentonite have not been fully understood. However, in a conceptual model proposed by several researchers, [17][18][19] the hydraulic conductivity is considered to be dominated by the ratio of mobile and immobile fractions of water in the bentonite sample; the former corresponds to the free water in macropores between montmorillonite particles, and the latter corresponds to the restricted one in electrical double layers (EDLs) formed over the surfaces of negatively charged montmorillonite particles. In general, the sizes of macropores increase as the dry density decreases, whereas the thickness of EDL can be affected by the pore water chemistry as indicated by the following equation,…”

Section: Resultsmentioning

confidence: 99%

A Study on Hydraulic Properties of Compacted Fe(III)-montmorillonite

Ito¹,

Miyasaka

Kozaki

et al. 2010

Journal of Nuclear Science and Technology

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Hydraulic conductivities were determined for compacted Fe(III)-montmorillonite sample. The Fe(III)-montmorillonite sample used in this study, which was prepared by the ion-exchange treatment of Namontmorillonite in FeCl 3 solution, contains less than 20% of Na þ ions as exchangeable cations and negligibly small amounts of iron precipitates. The measured hydraulic conductivities of compacted Fe(III)-montmorillonite were determined to be the order of 10 À9 , 10 À11 , and 10 À13 m s À1 at dry densities of 0.80, 1.01, and 1.20 Mg m À3 , respectively. These values were found to be kept constant during the experimental period, suggesting no significant change in the physicochemical properties of Fe(III)-montmorillonite during the experiment. When compared with Na-montmorillonite, remarkably high values of hydraulic conductivities were found for Fe(III)-montmorillonite at the dry densities of 0.8 and 1.0 Mg m À3 . On the other hand, almost the same value of hydraulic conductivity was obtained at the dry density around 1.2 Mg m À3 . This different effect of exchangeable cations on the hydraulic conductivity of montmorillonite could be attributed to the different sizes of macropores in compacted montmorillonite and/or the different thicknesses of electrical double layers formed over montmorillonite sheets.

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Section: Resultsmentioning

confidence: 99%

A Study on Hydraulic Properties of Compacted Fe(III)-montmorillonite

Ito¹,

Miyasaka

Kozaki

et al. 2010

Journal of Nuclear Science and Technology

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“…Since the hydraulic paths are longer than the specimen length, as mentioned before, however, the actual hydraulic gradient in the pores is smaller than the apparent hydraulic gradient. A relation between the apparent hydraulic gradient (I app ) and the actual hydraulic gradient in the pores (I ) can be expressed using the average laminated angle of the stacks (θ) (Tanaka et al 2009):…”

Section: Evaluation Of Hydraulic Conductivitymentioning

confidence: 99%

“…The same problems arose when the Kozeny-Carman relation was applied to bentonite and montmorillonite (Ren et al 2016;Kobayashi et al 2017;Kohno 2021). Tanaka et al (2009) proposed a model for hydraulic conductivity estimation that distinguished between interlayer pores and external pores. Their model, however, focused on high-effective montmorillonite density (the montmorillonite weight divided by the sum of the volumes of pores and montmorillonite) conditions and thus could not be applied under low-density conditions.…”

Section: Introductionmentioning

confidence: 99%

A model for estimating the hydraulic conductivity of bentonite under various density conditions

Kijima¹,

Sasagawa

Sawaguchi

et al. 2022

Hydrology Research

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Bentonite is an important material for low-permeability engineering systems used in dams and hazardous waste facilities. While models to characterize the hydraulic conductivity of bentonite have been developed in previous studies, these models were not applicable to various density conditions for Na- and Ca-bentonite. In this study, we present a new model for estimating the hydraulic conductivity of bentonite applicable to a wide range of density conditions for Na- and Ca-bentonite. In order to consider flow paths in compacted bentonite, a lamination structure of montmorillonite stacks was assumed. Our hydraulic model discriminated interlayer pores and other pores by applying a method for estimating the probability of connected pores and hydraulic coefficients governed by the plane Poiseuille flow equation. The model was consistent with the lower part of the experimental data investigated in previous studies on the hydraulic conductivity of Na-bentonite and was in good agreement with the data of Ca-bentonite in the range of an effective montmorillonite density (ρem) at 300 kg/m3 ≤ ρem ≤ 1,400 kg/m3 and 600 kg/m3 ≤ ρem, respectively. However, some experimental values on Ca-bentonite under low-density conditions were far higher than the model results in the case where Ca-bentonite forms flow paths of relatively large pores.

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“…13,14) In previous studies, the degree of chemical alteration of bentonite materials was often expressed based on the difference in the concentration of the solution used. 15,16) However, to the best of our knowledge, there have been no experimental studies on the swelling characteristics and permeability of bentonite based on variations in the montmorillonite content ratio due to chemical alteration.…”

Section: Introductionmentioning

confidence: 99%

Swelling Characteristics and Permeability of Bentonite-Based Materials Immersed in Various Solutions

Kohno

Nishimura

2022

Mater. Trans.

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Chemical alterations of bentonite are critical factors for the ultra-long-term stabilization of barriers and backfill in radioactive waste disposal. The chemical alterations may deteriorate the properties of bentonite-based materials. However, experimental studies on the effects of chemical alterations on the swelling characteristics and permeability of bentonite-based materials have not been investigated extensively. In this study, the effects of chemical factors on the swelling properties and permeability of bentonite-based materials were clarified based on one-dimensional swelling-pressure, hydraulic conductivity, X-ray powder diffraction patterns, and element mapping images. From the analytical and experimental results, a small amount of K + , Fe 3+ , and Mg 2+ can significantly deteriorate the swelling characteristic and permeability of bentonite-based materials in geological disposal (i.e., cause a decrease in swelling-pressure and an increase in hydraulic conductivity). Therefore, we conclude that it is necessary to pay close attention to the existence of these cations.

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Modeling Hydraulic Conductivity and Swelling Pressure of Several Compacted Bentonites Affected by Salinity of Water

Cited by 6 publications

References 12 publications

A Study on Hydraulic Properties of Compacted Fe(III)-montmorillonite

A Study on Hydraulic Properties of Compacted Fe(III)-montmorillonite

A model for estimating the hydraulic conductivity of bentonite under various density conditions

Swelling Characteristics and Permeability of Bentonite-Based Materials Immersed in Various Solutions

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