Hydraulic Conductivity And Swelling Properties Studies On Gaomiaozi Bentonite

Buffer/backfilling materials is one of the important components of engineered barriers for high-level radioactive waste(HLW)disposal repository, which plays an important role in filling the fractures in host rocks, preventing nuclides migration to surrounding rocks, supporting the waste container in proper position and preventing the underground water infiltrating into the waste container. Currently, bentonite is considered to be the best raw materils for buffer / backfill materials. Therefore, it is important to conduct the studies on physical and chemical properties, permeability and swelling properties of bentonite. The results of the studies could provide important technical parameters for repository design.Gaomiaozi bentonite(GMZ) in Inner Mongolia is selected as the raw materials for buffer/backfilling materials in HLW geological repository in China. On the basis of results from the previous studies of physical and chemical properties on GMZ, systematic studies on hydraulic conductivity and swelling properties with different hydraulic gradient, and with different compact densities, various grain sizes of GMZ samples have been conducted in this study.(1) The confined infiltration test results showed that hydraulic conductivity of GMZ bentonite is range from1.056×10-11m/s to 1.737×10-11m/s. The permeability could meet the requirements of buffer / backfill material in HLW disposal repository.(2) Dry compacted dry density is the main factor affecting the hydraulic conductivity, hydraulic conductivity will be decreased with the increase dry compacted density.(3) Under the same experimental conditions, the hydraulic conductivity will be increased with the increase of grain size of the bentonite samples.(4) The swelling force curve shows an asymptote with the change of time for highly compacted GMZ samples. And the experiments indicted that the swelling force of GMZ will be increased with the increase of dry compacted density, grain size, water content and the hydraulic gradient.(5) The hydraulic gradient is an important factor affecting the hydraulic conductivity of bentonite. The experiments approved that the percolation test with higher hydraulic gradient will lead to a lower hydraulic conductivity. Therefore, percolation test with lower hydraulic gradient is the proper way to obtain the actual hydraulic conductivity of bentonite.