Chemical impact on the hydro-mechanical behaviour of high-density FEBEX bentonite

The effect of the salinity of the saturating fluid on the hydro-mechanical properties of the FEBEX compacted bentonite was investigated by means of swelling, compressibility and permeability tests in which deionised water and solutions of different concentrations and compositions were used as saturating fluids. The solutions were chosen to simulate natural and extreme conditions in a high-level radioactive waste repository excavated in crystalline or clay host rocks. The swelling capacity of the bentonite decreases with the increase in salinity of the pore water, although this difference becomes less patent for high vertical loads and high densities and when the salinity of the solution is very low. The samples saturated with solutions containing high concentration of ions are also less deformable and consolidate more rapidly than the samples saturated with low-salinity solutions. The hydraulic conductivity of the highly compacted saturated FEBEX bentonite increases when high-salinity permeants are used, especially for low densities and when the stress level is low. The influence of the composition of the solution on the hydro-mechanical properties of the bentonite was also checked.