Effect of Initial Water Content and Dry Density on the Water Movement of the Compacted Bentonite

Concerning the geological disposal of high-level radioactive waste (HLW), understanding the water movement within compacted bentonite buffer material is essential for ensuring containment stability. This study explored how the dry density (ρ_d) and initial water content (w_i) of bentonite affect water diffusivity. In the experiments, water content (w) distributions within the bentonite specimen were measured after specific wetting durations. Applying the Boltzmann transformation with experimental data, a relationship between the water diffusion coefficient (D) and volumetric water content (θ) was derived and revealed that ρ_d and w_i have minor effects on D and D converges with increasing θ, irrespective of ρ_d and w_i variations. A simplified D−θ relation curve (D(θ) = 2.48 ± 0.25^e−0.030θ) was proposed, aligning well with experimental data on water content distributions in bentonite specimens. Simulations of the degree of saturation (S_r) over time demonstrated that S_r predictions varied within a 5% error margin with determined D boundaries, and converged as bentonite neared saturation, regardless of ρ_d and w_i.