Hydraulic conductivity of air-dried bentonite–sand blocks permeated with synthetic groundwater from radioactive waste repository

Laboratory experiments were conducted to evaluate the impact of drying cracks on hydraulic conductivity of compacted bentonite–sand blocks used as engineered barriers for radioactive waste disposal. Blocks were air-dried in an indoor environment to simulate the worst scenario without protection from drying during the interim storage and installation of the block. Synthetic groundwaters around the promising repository area were used as permeant solutions to study the hydraulic conductivity of air-dried blocks. Air-dried block samples were scanned by computed tomography (CT) before and after permeation to visualize the healing of drying cracks. Results show that swelling of the blocks was suppressed by the chemical components in the synthetic groundwater, and hydraulic conductivity of the block increased slightly (<4×) when permeated with the synthetic groundwater than those permeated with deionized water. Hydraulic conductivity of the air-dried block with cracks was slightly higher (<3×) than the hydraulic conductivity of the fresh block without cracks, indicating the remained swelling of the block permeated with synthetic groundwaters is sufficient to heal drying cracks. The healing of drying cracks was also quantified by CT images. These findings can increase the tolerance of drying cracks during block storage and installation.