Influence of salt concentration on volume shrinkage and water retention characteristics of compacted GMZ bentonite

The chemistry of pore water plays an important role on the hydraulic and mechanical properties of compacted bentonite used as buffer/backfill material in the repository of high-level radioactive waste (HLW). In this study, a series of compacted GMZ bentonite specimen with a dry density of 1.7 Mg/m(3) were prepared and initially saturated with NaCl solutions of different concentrations (0, 0.5, 1.0 and 1.5 mol/L), respectively. The drying process was brought forward on the specimens through increasing their suction by using vapor phase technique. During the drying process, the cracking behavior of the specimens was observed; the volume shrinkage and the water retention characteristics (WRCs) were investigated with the consideration of the chemistry. The results obtained show that the compacted specimen initially saturated with distilled water was observed with cracking when its suction increased to 82 MPa and others were found to crack off as their suctions increased to 139 MPa, while no cracks could be observed for the specimens below the suction of 82 MPa. For the confined specimens, volume shrinkage occurred with increase of the suction, accordingly changing their porosity; the void ratio of the specimens decreased as the suction of the soil increased and increased with the chemistry of the pore water. Meanwhile, the chemistry of the pore water has more significant impact on the WRCs of the specimens at a lower suction.