Swelling characteristics of compacted GMZ bentonite with saline-alkali evolution solutions

In the high-level radioactive waste repository, the concrete materials will decay into high-alkaline cement water under the long-term effects of groundwater and decay heat coupling, which then will affect the swelling characteristics of the compacted bentonite and may endanger the operation safety of the repository. According to the groundwater characteristics of the Beishan pre-selected disposal site in China, the Beishan site water (BSW), young cement water (YCW) and evolved cement water (ECW) are artificially prepared, respectively. At the same time, one-dimension swelling deformation tests are conducted on the compacted GMZ bentonite, the first choice of buffer/backfill materials for the repositories in China, with the infiltration of BSW, YCW and ECW. The evolution of swelling deformation characteristics of the compacted GMZ bentonite is analyzed considering the initial dry densities (1.50, 1.60, 1.70, 1.80 g/cm³) and the vertical stresses (0.1, 0.2, 0.4 MPa). The results show that with the infiltration of BSW, YCW and ECW solutions, the swelling deformation of the compacted GMZ bentonite continuously increases, but the rate of increase tapers off. The swelling deformation increases with the dry densities but decreases with the vertical stresses. On the basis of the micropores test results, the micro-mechanism of continuous swelling of the compacted bentonite samples caused by the infiltration of BSW, YCW and ECW solutions is analyzed. The results may provide a reference to the choice of buffer/backfill materials and the design for engineering barrier in the repositories in China.