Effects of specimen thickness on apparent swelling pressure evolution of compacted bentonite

Compacted bentonite is the main candidate for buffer material in several plans for spent nuclear fuel repositories. One of its important properties is high swelling capacity, which is caused by interaction between water molecules and exchangeable cations. This interaction makes bentonite behave differently from capillary materials. In this article, a model for thermo-hydro-mechanical state of partially water saturated bentonite is presented. It couples the water retention and swelling properties with introduction of the swelling factor in effective strain. The Helmholz energy density determines the state with a relatively small set of independent parameters: swelling pressure, swelling factor, maximum confined water content and the reference state. The model parameters are determined from experimental data for FEBEX bentonite, and as a simple consistency check, confined suction curves are calculated and compared to test results. Consistency of the model with observations on nano- and microscale of bentonite is also discussed.

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A Study on Gas Migration Behavior in Buffer Material using X-ray CT Method

MRS Proceedings ◽

10.1557/proc-932-114.1 ◽

2006 ◽

Vol 932 ◽

Author(s):

K. Tanai ◽

M. Yui

Keyword(s):

Water Saturation ◽

Gas Injection ◽

Swelling Pressure ◽

Digital Data ◽

Migration Behavior ◽

Gas Migration ◽

Migration Test ◽

X Ray ◽

Compacted Bentonite ◽

Buffer Material

ABSTRACTThis paper presents a study on gas migration behavior in a bentonite specimen with the aid of X-ray computer tomography (CT) scan data. The laboratory experiment was carried out to clarify gas migration behavior through saturated, compacted bentonite. X-ray CT was used to estimate the spatial distribution of gas and water saturation during gas migration test in the bentonite. For the gas migration test, the controlled flow rate of gas injection was adopted for pre-compacted samples of Kunigel V1 bentonite using helium gas, which is safer than hydrogen gas.A specimen was isotropically consolidated and saturated by synthetic seawater, simultaneously, by applying a backpressure. This was followed by injecting the gas using a syringe pump. Inlet and outlet gas fluxes were monitored. This test exhibited a significant threshold pressure for breakthrough, somewhat larger than the sum of the swelling pressure and the backpressure.The procedure of the X-ray CT measurement is as follows; i) measurement of the initial condition (saturated condition) of the compacted bentonite, ii) measurement of the gas injection condition as a function of time. The digital data obtained from the X-ray CT usually includes some noise. The stacking method can reduce the noise in CT values and enables to identify the gas migration area. The results indicate that gas is transported through preferential pathways in compacted bentonite, and is not homogenous.

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New equations for swelling characteristics of bentonite-based buffer materials

Canadian Geotechnical Journal ◽

10.1139/t02-115 ◽

2003 ◽

Vol 40 (2) ◽

pp. 460-475 ◽

Cited By ~ 71

Author(s):

Hideo Komine ◽

Nobuhide Ogata

Keyword(s):

Double Layer ◽

Nuclear Waste ◽

Van Der Waals ◽

Swelling Pressure ◽

Van Der Waals Force ◽

Diffuse Double Layer ◽

Mass Ratio ◽

Compacted Bentonite ◽

Buffer Material ◽

Swelling Characteristics

Compacted bentonite and sandbentonite mixtures are attracting greater attention as buffer material for repositories of high-level nuclear waste. This buffer material is expected to fill up the space between the canisters containing the waste and the surrounding ground by swelling. To produce the specifications, such as dry density, sandbentonite mass ratio, and dimensions, of the buffer material, the swelling characteristics of compacted bentonite and sandbentonite mixtures must be evaluated quantitatively. New equations for evaluating the swelling behavior of compacted bentonite and sandbentonite mixtures are presented that can accommodate the influences of the sandbentonite mass ratio and the exchangeable-cation composition of bentonite. The new method for predicting swelling characteristics is presented by combining the new equations with the theoretical equations of the GouyChapman diffuse double layer theory and of the van der Waals force, which can evaluate the repulsive and attractive forces of montmorillonite mineral (i.e., the swelling clay mineral in bentonite). Furthermore, the applicability of the new prediction method has been confirmed by comparing the predicted results with laboratory test results on the swelling deformation and swelling pressure of compacted bentonites and sandbentonite mixtures.Key words: bentonite, diffuse double layer theory, van der Waals force, nuclear waste disposal, swelling deformation, swelling pressure.

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Swelling pressure of compacted bentonite acting on constraining material with deformability

Géotechnique ◽

10.1680/jgeot.20.p.348 ◽

2021 ◽

pp. 1-10

Author(s):

Yasutaka Watanabe ◽

Yukihisa Tanaka

Keyword(s):

Swelling Pressure ◽

Compacted Bentonite

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

ASME 2010 13th International Conference on Environmental Remediation and Radioactive Waste Management, Volume 2 ◽

10.1115/icem2010-40013 ◽

2010 ◽

Cited By ~ 1

Author(s):

Yukihisa Tanaka ◽

Takuma Hasegawa ◽

Kunihiko Nakamura

Keyword(s):

Hydraulic Conductivity ◽

Radioactive Waste ◽

Ground Water ◽

Quantitative Evaluation ◽

Coastal Area ◽

Evaluation Method ◽

Saline Water ◽

Swelling Pressure ◽

Compacted Bentonite ◽

Swelling Characteristics

In case of construction of repository for radioactive waste near the coastal area, the effect of salinity of water on hydraulic conductivity as well as swelling pressure of bentonite as an engineered barrier should be considered because it is known that the hydraulic conductivity of bentonite increases and swelling pressure decreases with increasing salinity of water. Though the effect of salinity of water on hydraulic conductivity and swelling pressure of bentonite has been investigated experimentally, it is necessary to elucidate and to model the mechanism of the phenomenon because various kinds of bentonites may possibly be placed in various salinities of ground water. Thus, in this study, a model for evaluating hydraulic conductivity as well as swelling pressure of compacted bentonite is proposed considering the effect of salinity of water as follows: a) Change in number of flakes of a stack of montmorillonite because of cohesion. b) Change in viscosity of water in interlayer between flakes of montmorillonite. Quantitative evaluation method for hydraulic conductivity and swelling characteristics of several kinds of bentonites under saline water is proposed based on the model mentioned above.

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