The impact of multi-component hypersaline wetting on soluble and exchangeable cations and water retention behaviour of MX80 bentonite

The impact of multi-component hypersaline groundwater is simulated by synthetic hypersaline water with 330 g/L total dissolved solids and an osmotic suction of 41 MPa. The effects of this hypersaline water on the retention behavior of compacted MX80 and MX80/poorly graded sand mixtures as well as MX80 amounts and distributions of soluble and exchangeable cations, and their valences were investigated. Wetting path unconfined condition total suction measurements on pre-hydrated and compacted specimens were reported for MX80 and MX80/sand mixtures prepared at different dry densities and water contents with deionized and hypersaline water. The hypersaline water had no effect on total suction and soluble cations until about 13% gravimetric water content and then the effect gradually increased up to a gravimetric water content of 18%, at which point the total suction values of MX80 were dominated by the osmotic suction of the pore fluid. For the levels of initial compaction and percentages of MX80 in the mixture studied, there was no clear change in the total suction for MX80 gravimetric water contents greater than about 18%. It is indicated that the effect of hypersaline pore fluid should be considered in designing deep geological repositories in a highly saline environment.