Abstract: Compacted bentonite is widely used as a hydraulic barrier in municipal landfills and deep geological repositories for nuclear waste. However, long-term exposure to salt-bearing pore fluids can substantially increase its permeability, thereby threatening the barrier integrity and containment safety. Therefore, developing a theoretical model that quantitatively describes how permeability depends on salt concentration and mechanical loading is critical for performance prediction. In this study, we investigate the microstructure of bentonite fully saturated with saline solutions, focusing on the alteration of interlayer and inter-aggregate pores induced by variations in ionic strength. We then revise the conventional relationship between permeability and montmorillonite void ratio by explicitly considering the salt effects on the diffuse double layer and interparticle forces. Additionally, a modified effective stress is introduced to account for physicochemical interactions, and a fractal model is formulated to capture the coupled influences of overburden pressure and solution concentration on the permeability. The fractal dimension in the model reflects the tortuosity and connectivity of the pore network, both of which are sensitive to salt concentration. The model is validated using experimental data from our consolidation-permeability tests and from previously reported studies, covering a range of NaCl concentrations and effective stress levels. The comparison demonstrates that the relative errors between the predicted and measured values are within ±12%, and the overall agreement is highly satisfactory. The proposed model provides a simple, reliable, and physically grounded tool for estimating the evolution of bentonite permeability under chemically aggressive conditions, thereby facilitating long-term safety assessment and engineering design.

Key words: compacted bentonite, saline solution, permeability coefficient, fractal, consolidation test