The use of high-density bentonite-sand mixtures as buffer and sealing materials at the disposal sites of radioactive waste is expected. Although the bentonite–sand mixtures at disposal sites will be in an unsaturated condition during the construction period, they will gradually become saturated by reflooding in the ground water after the service commencement. In the present paper, a series of fully undrained triaxial tests is performed to make clear the shear properties of a high-density bentonite–sand mixture. In the case of a low degree of saturation, the shear strength is relatively large and volumetric expansion is observed. However, in the case of a high degree of saturation, the shear strength is small and volumetric compression is observed. These results suggest that the mechanical properties of high-density bentonite rapidly change with an increasing degree of saturation.

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Bentonite-based buffer for high-level radioactive waste (HLW) disposal is expected to fill the interstitial spaces around buffer materials by its swelling deformation. This study performs one-dimensional model tests simulating the relation around the buffer and evaluates the self-sealing capability of the buffer quantitatively. It also investigates the applicability of the theoretical equations for evaluating the swelling characteristics of a bentonite-based buffer, first proposed by Komine and Ogata, to analysis of the self-sealing capability by comparing the calculated and experimentally obtained results. Furthermore, this study has shown the design flow for specifications of bentonite-based buffer from the viewpoint of self-sealing capability.

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Safety of great deep repository design has been considered for high level radioactive waste disposal system in several countries such as Belgium, Canada, China, France, Germany, Japan, Sweden and Switzerland etc. The repository of the disposal is in most cases based on the aspect of multi-barrier system such as the natural barrier formation (i.e., host rock) and engineered barrier formation consisting of compacted bentonite. This study focuses on hydro-mechanical behavior of compacted sodium bentonite, and three different tests such as swelling test, one-dimensional compression test and constant vertical stress direct shear test were performed with suction control using vapor pressure technique. Also, a modified direct shear apparatus installed RH air circulation system was used in the direct shear test.

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The 2011 accident of Fukushima-Daiichi nuclear power plant caused radioactive contamination of surface soil and waste by fall-out of radioactive chemicals such as ¹³⁴Cs and ¹³⁷Cs. In disposal of soils and solid wastes containing low-levels of radioactive chemicals at existing MSW (municipal solid waste) landfills, installation of soil layers, such as excavated soils or bentonite amended soils, which act as sorption layers against radioactive cesium, has been planned. This manuscript addresses the results on a series of batch sorption/desorption tests to assess the effects of major cations in the leachate from MSW incinerator fly ash (MSWIFA) on the cesium sorption/desorption characteristics of sodium bentonite. The testing results indicated that major cations existing in the MSWIFA leachate such as sodium, potassium and calcium ions significantly reduced the cesium sorption capacity, and the higher concentrations led to the lower K_d values, which were two orders lower than that for the distilled water when these cation concentration was higher than 10 meq/L. Particularly, calcium ion was most likely to inhibit the fixation of cesium rather than potassium and sodium ions, and the calcium ion concentration of the leachate was a good index to explain the adverse effect on the cesium sorption. Similarly, calcium and potassium ions most significantly promoted the desorption of cesium once fixed to the bentonite, more than 30% of which was desorbed when the leachate contained 10 meq/L of calcium or potassium ions.

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This paper studies the effects of bio-clogging on hydraulic conductivity of compacted soils used as landfill liners. Landfill leachate contains a large amount of microorganism and bacterial biomass, which was likely to cause bio-clogging in landfill liners. To interpret the effect of bio-clogging on hydraulic property of compacted clays, in this study, a series of laboratory-scale hydraulic conductivity tests were conducted. The long term hydraulic conductivity of compacted clays was measured with distilled water, landfill leachate and one type of nutrient solution. The laboratory test results show that the hydraulic conductivity of compacted clays permeated with distilled water stabilized at approximately 3.77 × 10-8 cm/s, and the hydraulic conductivity of compacted clays permeated with landfill leachate or nutrient solution ranged between 1.1 × 10-8 cm/s and 5.22 × 10-9 cm/s. Such a significant difference was attributed to the effect of bio-clogging. The microorganism and bacterial biomass reduced the hydraulic conductivity up to one order of magnitude. This study indicated that the bio-clogging is approximately a feasible method to create low-cost and low-hydraulic conductivity barriers by using locally available clayed soils.

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Studies for analysis of deformation behavior of geosynthetics suspending over voids in landfills are very limited, especially for situations in which several voids are closely distributed. Hence, the main objective of this paper is to study the behavior of geosynthetics over voids in a landfill. The coupling effect of two adjacent voids on geosynthetics and the simplified interface friction formula between geosynthetic and soil being considered, an analytical model is established to calculate the deformation of geosynthetics. Compared to the situation of two uncoupled cracks, the maximum strain of geosynthetics is greater and the maximum settlement is smaller when the two voids are coupled.

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The objective of this study was to evaluate the change in the barrier performance of a geosynthetic clay liner (GCL) as a result of desiccation due to dehumidification at 55°C. Specimens of GCL that were damaged by desiccation were scanned using a micro-focused X-ray computed tomography (CT) scanner, and crack generation under two different dehumidification conditions was examined using the results of image analysis. Permeability tests were performed to estimate the hydraulic conductivity of GCL damaged by desiccation with respect to a calcium chloride solution. The results obtained indicate that dehumidification and a space between a GCL and a membrane sheet are key factors in the generation of cracks in the bentonite layer of a GCL at 55°C.

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