Test on soil-water characteristic curves of bentonite-sand mixtures

In the geological disposal of high-level radioactive waste (HLW), the performance of the cushioning material will improve when the bentonite is mixed with a certain proportion of quartz sand. A research on soil-water characteristic curves of compacted mixture of bentonite-sand for higher suctions is carried out through moisture balance method; and influences of temperature, sanding rate and dry density on water retention capacity of the bentonite-sand mixture are analyzed. The results show that the water retention capacity of the mixture decreases obviously with temperature increase. Within the controlled suction range, the influence of sand mixing ratio on the soil-water characteristic curve is evident when suction is low; Within the controlled suction range, the influence of sanding rate on the soil-water characteristic curve is evident when suction is low, and at high suction the effects gradually decreased. On the other hand, dry density almost has no effect on the soil-water characteristic curve. Empirical formulas for SWCCs of bentonite-sand mixed buffer/backfill material under conditions of different temperatures and sanding mixing ratio are proposed by fitting the experimental data; and SWCCs of this material with different temperatures can be thus predicted.