Predicting hydraulic conductivity of sand–bentonite mixture backfill before and after swelling deformation for underground disposal of radioactive wastes

Mixtures of sand and bentonite will be used as bentonite-based backfill materials for high-level radioactive waste repositories. They are also used in Japan as artificial barriers in disposal facilities for low-level radioactive waste. Very low hydraulic conductivity of the sand–bentonite mixture is expected to keep wastes separated from the surrounding environment. Some researchers have investigated hydraulic conductivities of sand–bentonite materials at different dry densities and at different mass ratios of sand and bentonite to design and develop specifications of the materials described above.However, the function of low permeability of those materials is degraded by the altered hydraulic conductivity of sand–bentonite mixtures after swelling deformation. This study investigates experimentally hydraulic conductivity changes before and after swelling for sand–bentonite materials. Furthermore, results confirm the applicability of theoretical equations for evaluating the hydraulic conductivity of compacted bentonites and sand–bentonite mixtures, which have already been proposed in Komine (2008), by comparing calculated results and experimental results.