Swelling behavior of compacted bentonite-sand mixture during water infiltration

A laboratory-based water infiltration test was conducted with compacted Calcigel bentonite-sand mixture (50:50) at room temperature to mimic the transient hydration of a backfill material in nuclear waste repository conditions. The test was performed with an innovative column-type experimental device, which facilitated the continuous and non-destructive measurements of temperature, relative humidity, water content and total stresses in both axial and lateral direction at various preselected locations along the height of soil sample. The effect of groundwater geochemistry on the bentonite hydration process was not considered in this study. The distilled water was supplied from the bottom-end under 15-kPa hydration pressure for a period of 349 days to mimic the water ingress from the host rock. The test results highlighted the hydration-induced heterogeneity in the material and its effect on the lateral swelling pressure development along the height of soil sample. The axial swelling pressure measurements revealed the factors, which affect the stress-transfer mechanism between both the ends. The simultaneous measurements of relative humidity and water content indicated the porosity redistribution close to the hydration-end during the test.