• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.179-187
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• 2009

Bentonite-based grouting has been popularly used to seal a borehole installed for a closed-loop vertical ground heat exchanger in a geothermal heat pump system (GHP) because of its high swelling potential and low hydraulic conductivity. The bentonite-based grout, however, has relatively lower thermal conductivity than that of ground formation. Accordingly, it is common to add some additives such as silica sand to the bentonite-based grout for enhancing thermal performance. In this study, graphite is adapted to substitute silica sand as an addictive because graphite has very high thermal conductivity. The effect of graphite on the thermal conductivity of bentonite-based grouts has been quantitatively evaluated for seven bentonite grouts from different product sources. In addition, comparisons of viscosity between applications of graphite and silica sand as additives has been carried out. In conclusion, using graphite has thermal conductivity about three times higher than that of silica sand.

• Journal of the Korean GEO-environmental Society
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• v.11 no.4
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• pp.5-12
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• 2010

Soil mixture using bentonite as a cutoff material is used a lot for various structures such as landfills, banks and dams as cutoff materials. But seepage water is expected to seep since shear failure of filter layer occurs due to external load, embankment load when constructed. Generally, only coefficient of permeability of Soil Mixture is considered irrespective of the changes of intensity on amount of additives. This research is to study on how the changes of amount of bentonite affects permeability and strength of soil mixture. So successive experiments for measuring permeability and strength were conducted as the amount of bentonite changes from 0 to 4%, mixing with the bed material and then making specimens. Around construction site of B dam. As a result, 2.085E-07 cm/sec was shown when the amount of Soil Mixture was 4%. It is proved that unconfined compressive strength and tensile strength increase as the amount of bentonite increases, but saturation shear strength of bentonite soil mixture from the CD experiment is hardly influenced by the amount of bentonite.

• Journal of the Korean Geotechnical Society
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• v.22 no.1
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• pp.45-52
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• 2006

A theoretical equation, from which we can get a suitable ratio of bentonite at bentonite-mixed soil, was derived for desigri of the impermeable condition. Bentonite is a soil with great expansion property and it has the permeability lower than $1\times10^{-7}cm/sec$ in spite of its maximum expansion state. Accordingly if the void of soil is filled with the liquid of bentonite, water will flow only through the veid of bentonite liquid. And the permeability of bentonite-mixed soil will always satisfy the condition as impermeable zone. However, because it is very difficult to mix uniformly bentonite with soil, it is thought that the actual mixing ratio fur the impermeable zone will be grater than that by theoretical equation. Permeability tests were performed to check the equation and a modified equation was suggested from the experimental results.

• Journal of the Korean Geotechnical Society
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• v.23 no.7
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• pp.47-55
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• 2007

In this study, applicability of electrical conductivity monitoring technique for containment barrier such as soil-bentonite wall was evaluated. Laboratory tests including permeability tests and column tests were performed to understand variations in electrical conductivity at different bentonite contents, hydraulic conductivities, and heavy metal concentrations. The electrical conductivity of compacted soil-bentonite mixtures was found to increase proportionally with bentonite content. Accordingly, the hydraulic conductivity of compacted soil-bentonite mixtures which decreases linearly with increasing bentonite content was found to have an inversely proportional relationship with the electrical conductivity. In column tests, electrical conductivity breakthrough curves and concentration breakthrough curves were simultaneously obtained. These results indicated that electrical conductivity measurement can be an effective means of detecting heavy metal transport at the desired locations within barriers and verifying possible contaminant leakage. Experimental results obtained from this study showed that the electrical conductivity measurement can be a promising tool for monitoring of containment barrier.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.561-577
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• 2021

The compacted bentonite buffer in a geological repository for high-level radioactive waste disposal is saturated due to groundwater inflow. Saturation of the bentonite buffer results in bentonite swelling and bentonite penetration into the rock discontinuities present around the disposal hole. The penetrated bentonite is exposed to groundwater flow and can be eroded out of the repository, resulting in bentonite mass loss which can affect the physical integrity of the engineered barrier system. Hence, the evaluation of buffer-rock interactions and coupled behavior due to groundwater inflow and bentonite penetration is necessary to ensure long-term disposal safety. In this study, the effects of the bentonite penetration and swelling on the physical properties of jointed rock mass were evaluated using the quasi-static resonant column test. Jointed rock specimens with bentonite penetration were manufactured using Gyeongju bentonite and hollow cylindrical granite rock discs obtained from the KAERI underground research tunnel. The effects of vertical stress and saturation were assessed using the P-wave and S-wave velocities for intact rock, jointed rock and jointed rock with bentonite penetration specimens. The joint normal and joint shear stiffnesses of each joint condition were inferred from the wave velocity results assuming an equivalent continuum. The joint normal and joint shear stiffnesses obtained from this study can be used as input factors for future numerical analysis on the performance evaluation of geological waste disposal considering rock discontinuities.

• Geotechnical Engineering
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• v.13 no.2
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• pp.9-16
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• 1997

Cut-off methods of controlling leachate migration from waste landfills and contaminated sites are studied. Permeability and chemical compatibility tests are prrforlned on slurry wall materials including soil-bentonite, cement-bentonite, cement / fly ash-bentonite, plastic concrete. Hydraulic conductivity of soil-bentonite mixture is the lowest of these four bacuill materials. The leachate from municipal solid waste has little influence on the permeability of the backfill materials. The bentonite slurry becomes flocculated and aggregated when exposed to the leachate. The results of the permeability test showed that the hydraulic conductivities of the backfill materials are in the order soil-beiltonite, Plastic concrete, cement-bentonite. And the result c: the compatibility test showed increase in permeability due to the effects of leachate. Thus, in designing the slurry wall it is essential to check the behaviour of the bentonite slurry and backfill materials on the compatibility with the contaminants.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.14 no.1
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• pp.1-9
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• 2016

In this study, thermal-hydrological-chemical modeling for the alteration of a bentonite buffer is carried out using a simulation code TOUGHREACT. The modeling results show that the water saturation of bentonite steadily increases and finally the bentonite is fully saturated after 10 years. In addition, the temperature rapidly increases and stabilizes after 0.5 year, exhibiting a constant thermal gradient as a function of distance from the copper tube. The change of thermal-hydrological conditions mainly results in the alteration of anhydrite and calcite. Anhydrite and calcite are dissolved along with the inflow of groundwater. They then tend to precipitate in the vicinity of the copper tube due to its high temperature. This behavior induces a slight decrease in porosity and permeability of bentonite near the copper tube. Furthermore, this study finds that the diffusion coefficient can significantly affect the alteration of anhydrite and calcite, which causes changes in the hydrological properties of bentonite such as porosity and permeability. This study may facilitate the safety assessment of high-level radioactive waste repositories.

• Transactions of Materials Processing
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• v.12 no.5
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• pp.479-486
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• 2003

This paper presents an elastoplastic analysis for spent nuclear fuel disposal container and its 50 cm thick bentonite buffer to predict the collapse of the container while the horizontal asymmetric sudden rock movement of 10 cm is applied on the composite structure. This sudden rock movement is anticipated by the earthquake etc. at a deep underground. Elastoplastic material model is adopted. Drucker-Prager yield criterion is used for the material yield prediction of the bentonite buffer and von-Mises yield criterion is used for the material yield prediction of the container. Analysis results show that even though very large deformations occur beyond the yield point in the bentonite buffer, the container structure still endures elastic small strains and stresses below the yield strength. Hence, the asymmetric 50 cm thick bentonite buffer can protect the container safely against the 10 cm sudden rock movement by earthquake etc.. Analysis results also show that bending deformations occur in the container structure due to the shear deformation of the bentonite buffer. The finite element analysis code, NISA, is used for the analysis.

• Textile Coloration and Finishing
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• v.33 no.3
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• pp.161-167
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• 2021

Polymer nanocomposite is considered a great alternative to solve the limitations that exist in a simple combination material, as well as to produce multifunctional and high-performance results. In this research, PVA/bentonite nanocomposite films were prepared based on the presence or absence of modification of nano-clay(bentonite) a SUPERGEL^® product, modification conditions and content, and the structural variation of the prepared PVA/bentonite nanocomposite films were examined. The effect of variations in the internal structure of the nanocomposite on mechanical and thermal properties was investigated. As a result of evaluating the thermal characteristics of the PVA/bentonite nanocomposite film based on the concentration of the modified bentonite, it was verified that the thermal characteristics and stability were improved because of interaction between the polymer and the modified nano-clay.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.20 no.1
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• pp.1-12
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• 2022

Bentonite is the most probable candidate to be used as a buffer in a deep geological repository with high swelling properties, hydraulic conductivity, thermal conductivity, and radionuclide sorption ability. Among them, the radionuclide sorption ability prevents or delays the transport of radionuclides into the nearby environment when an accident occurs and the radionuclide leaks from the canister, so it needs to be strengthened in terms of long-term disposal safety. Here, we proposed a surface modification method in which some inorganic additives were added to form NaP zeolite on the surface of the bentonite yielded at Yeonil, South Korea. We confirmed that the NaP zeolite was well-formed on the bentonite surface, which also increased the sorption efficiency of Cs and Sr from groundwater conditions. Both NaP and NaX zeolite can be produced and we have demonstrated that the generation mechanism of NaX and NaP is due to the number of homogeneous/heterogeneous nucleation sites and the number of nutrients supplied from an aluminosilicate gel during the surface modification process. This study showed the potential of surface modification on bentonite to enhance the safety of deep geological radioactive waste repository by improving the radionuclide sorption ability of bentonite.