Gas transport in granular compacted bentonite: coupled hydro-mechanical interactions and microstructural features

Gonzalez‐Blanco, Laura; Romero, E.; Marschall, Paul

doi:10.1051/e3sconf/202019504008

Cited by 8 publications

(13 citation statements)

References 13 publications

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“…2). Gonzalez-Blanco & Romero (2019) [10] observed a large number of fissures between large-size granules in compacted GB after freeze-drying, using Micro-CT (Fig. 4c).…”

Section: Microstructural Analysismentioning

confidence: 87%

“…In the CT image of bentonite materials (Fig. 2), the voxels with darker colours represented low-density phases such as air or water, while those with brighter colours indicated high-density solid particles [10]. The CT slices of the compacted bentonite samples with different water contents revealed the microstructure under ascompacted states, with local heterogeneity in bulk density distribution.…”

Section: Microstructural Analysismentioning

confidence: 97%

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Microstructure and hydro-mechanical behaviour of compacted granular bentonite

et al. 2023

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In recent years, granular bentonite GB has become a reference material since it facilitates the backfilling operation due to high-density compacted granules with extended grain size distribution(maximum sizes around 10 mm). This investigation explores the initial microstructure of MX80-type GB and the hydro-mechanical HM response observed at the phenomenological scale. Samples were statically compacted at a fixed dry density (1.55 Mg/m3 ), encompassing dry and wet sides of the optimum. Themicrostructural study was performed using a combination of X-ray micro-computed tomography and mercury intrusion porosimetry. The results indicate that the pore size density function of compacted GB can be simplified as a double-porosity network with micropores (intra-granular/aggregate pores) and macropores(inter-granular/aggregate pores). Compacting at the dry side increases macropores, making the sample more compressible on loading under as-compacted states despite the higher matric suction. The time evolution of the swelling pressure displays a double-peak pattern attributed to the particular microstructure of the samples. Moreover, the initial microstructure does not significantly influence the water retention properties without a marked hysteresis in the high-suction range under confined wetting/drying cycles. This work’s outcomes highlight the microstructure’s significance in the HM behaviour of compacted GB and provide further insight into the geotechnical properties of this material.

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“…2). Gonzalez-Blanco & Romero (2019) [10] observed a large number of fissures between large-size granules in compacted GB after freeze-drying, using Micro-CT (Fig. 4c).…”

Section: Microstructural Analysismentioning

confidence: 87%

Section: Microstructural Analysismentioning

confidence: 97%

Microstructure and hydro-mechanical behaviour of compacted granular bentonite

et al. 2023

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“…Dry air was used as the injection gas. The tests were carried out at constant total vertical stress or constant volume in a high-stress oedometer cell [10]. The setup of the gas dissipation test at constant injection gas volume and the auxiliary devices are presented in Figure 3.…”

Section: Methodsmentioning

confidence: 99%

Gas transport in a binary bentonite mixture used in sealing systems

2023

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Binary mixtures composed of 80% of high-density pellets and 20% of granular bentonite at hygroscopic water content are currently considered for use in vertical sealing systems for the deep and longterm disposal of radioactive wastes. By pouring the dry components without compaction, the mixturedisplays a dry density of around 1.49 Mg/m3. However, these sealing systems are subjected to long-term hydrations from the surrounding formations with the possibility of having zones with entrapped and generated gas that makes it challenging to display a homogeneous saturation of the seal. Therefore, gas transport through these bentonite-based sealing materials at different degrees of saturation is a crucial issue. Hence, several oedometer tests have been conducted to evaluate the impact of gas injection on this mixture at different degrees of saturation and constant pouring dry density. These gas injection/dissipation tests were performed at constant vertical stress or constant volume conditions. The results provided the variation of the effective gas permeability at different degrees of saturation and the gas breakthrough pressure aftersaturation. Furthermore, these gas transport results were interpreted with a microstructural study of the mixture focusing on the volumetric filling of the inter-pellet porosity.

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“…The conceptual model, based on a laboratory experiment in Ref. [30], consists of a bentonite sample enclosed on two sides by a filter material (Figure 9, left). A heterogeneous distribution of Young's modulus is derived from MIP data for the bentonite sample (Figure 9, right).…”

Section: Gas Migration In Clayey Materialsmentioning

confidence: 99%

Coupled Processes at Micro- and Macroscopic Levels for Long-Term Performance Assessment Studies of Nuclear Waste Repositories

Shao,

Radeisen,

Hesser

et al. 2024

Minerals

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Performance assessment of nuclear waste repositories requires state-of-the-art knowledge of radionuclide transport properties. Additionally, the short-term development under thermal pulses and the long-term development of the near field—due to influences such as gas generation—must be evaluated. Key thermal-hydro-mechanical-chemical processes are strongly coupled on different spatial and temporal scales. To understand these coupling mechanisms, numerous material models and numerical codes have been developed. However, the existing constitutive approaches—which have been adapted to describe small-scale laboratory experiments and validated against real-scale field observations—are often unable to capture long-term material behavior with sufficient precision. To build the confidence, a more comprehensive understanding of the system at micro- and macroscopic scales is required. Most observed macroscopic processes result from microscopic changes in the crystal structure and/or crystalline aggregates, as well as changes in material properties under the influence of various factors. To characterize these physical fields in crystals, microscopic investigations, such as visualization, or geophysical methods are introduced to verify the understanding at the microscale. Two cases are demonstrated for the presented concept using microscale information: one deals with the mechanically and thermally driven migration of fluid inclusions in rock salt, the other with dilatancy-controlled gas transport in water-saturated clay material.

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Gas transport in granular compacted bentonite: coupled hydro-mechanical interactions and microstructural features

Cited by 8 publications

References 13 publications

Microstructure and hydro-mechanical behaviour of compacted granular bentonite

Microstructure and hydro-mechanical behaviour of compacted granular bentonite

Gas transport in a binary bentonite mixture used in sealing systems

Coupled Processes at Micro- and Macroscopic Levels for Long-Term Performance Assessment Studies of Nuclear Waste Repositories

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