Effects of solution concentration and vertical stress on the swelling behavior of compacted GMZ01 bentonite

Compacted bentonite has been considered as buffer/backfill material in radioactive waste disposal. This study deals with the effects of the concentration of infiltration saturation and vertical stress on the swelling behavior of compacted GMZ bentonite. One-dimensional swelling tests were performed on specimens at an initial dry density of 1.7 Mg/m3. NaCl solutions with concentrations of 0 (de-ionized water), 0.1, 0.5 and 1.0 mol/L were used to saturate the specimens while three vertical stresses of 0.06, 0.062 and 1.85 MPa were applied. Results show that, for all the infiltration solutions, the swelling strain decreases with increasing vertical stress; the impact of the vertical stress is more significant for low vertical loads while it is less patent when the high salinity solution is infiltrated. For all the vertical stresses applied, the swelling strain decreases with the increase in concentration of the infiltration solution; the impact of the concentration of infiltration solution is not only related to the vertical stress, but also to the soil permeability. Furthermore, the coefficient of primary swelling decreases with the increase in concentration and vertical stress. The concentration of infiltration solution has significant restricting effect on the secondary swelling deformation in case of low vertical stress, while it has no or few effects on the secondary swelling deformation in case of higher vertical stress.