Swelling and gas transport characteristics of saturated compacted bentonite/sand samples considering the scale effect

The generation and migration of gas is an unavoidable process that should be considered in the safety evaluation of nuclear waste geological repositories. The first aim of this study is to determine whether the gas will affect the swelling and sealing properties of the bentonite-based barrier. The results show that the gas/water can significantly affect the pore pressure of the material, which can further affect the total pressure of the compacted bentonite/sand sample. There exists a mathematical relationship between the gas pressure, total pressure, and effective swelling pressure. Furthermore, the influence of the size effect on the swelling properties and gas breakthrough properties of compacted bentonite/sand mixture was also investigated. The change in the sample's size has a limited impact on the swelling pressure of the sample, but delays the water saturation process. Concerning the gas breakthrough properties, the influence of the sample's size is also not apparent. Finally, the results of laboratory experiments are compared with the results of in situ experiments. The results show that the laboratory experiments have a good reference value based upon the key indicators, such as swelling pressure, water gas permeability, and gas breakthrough pressure. This means that the results obtained from the small-scale laboratory experiments are reliable and can be referenced for the in situ design of the nuclear waste geological repository. (C) 2020 Elsevier Ltd. All rights reserved.