A gas permeability model for unsaturated bentonite considering the stress and temperature effects

Gas permeability is a crucial parameter for assessing the long-term gas tightness of bentonite in deep geological repositories. Although extensive experimental work has been conducted, there remains a deficiency in models capable of describing the variations in its gas permeability, particularly when considering the impacts of stress and temperature. This study presents a gas permeability model that directly addresses the initial relative humidity (RH), stress, and temperature conditions of unsaturated bentonite, utilizing a perspective grounded in the double pore structure. Validation of the model encompasses three key aspects: water retention characteristics, alterations in gas permeability under varying stress levels, and gas permeability fluctuations corresponding to temperature changes under constant stress conditions. The findings indicate that the model adeptly captures the variations attributable to each factor, enabling the quantitative assessment of gas permeability across multiple scales. The model parameters closely correlate with the material's hydraulic history, facilitating a consistent description through establishing a relationship with suction. This approach achieves a standardized quantification of gas permeability. Notably, the model can potentially simulate the evolution of gas permeability in compacted bentonite in deep geological disposal of high-level waste (HLW).