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 (rho d) and initial water content (wi) 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 (theta) was derived and revealed that rho d and wi have minor effects on D and D converges with increasing theta, irrespective of rho d and wi variations. A simplified D-theta relation curve (D(theta) = 2.48 +/- 0.25e-0.030 theta) was proposed, aligning well with experimental data on water content distributions in bentonite specimens. Simulations of the degree of saturation (Sr) over time demonstrated that Sr predictions varied within a 5% error margin with determined D boundaries, and converged as bentonite neared saturation, regardless of rho d and wi.