Advances in studies on pore structure of highly compacted bentonite

Based on the detailed description of pore structure of highly compacted bentonite and approaches used to determine delimiting diameter, the evolution of pore structure under the near-field environment in repository and its influence on hydraulic behavior of the bentonite are summaried. The results show that the pore structure is made up of three classes of pores, including inter-layer, inter-particle and inter-aggregate pores. When describing the constitutive model for bentonite, the pore structure is always simplified as dual pore structure consisting of macro-and micro-pores. The approaches used to determine the delimiting diameter have not reached a consensus. The evolution of pore structure is affected by the near-field conditions of deep geological repository, including temperature, seepage, stress and chemical fields. However, less studies have considered the influences of multi-field coupling on the evolution. The pore ratio and pore-size distribution cannot accurately reflect the actual pore structure, especially the pore shape and spatial distribution. Hence, there are some limitations when the pore ratio and pore-size distribution are used to explore the relationship between the pore structure and the hydraulic behavior of the bentonite. Based on the above, the following aspects should be deeply studied in the future: the optimal approach used to determine the delimiting diameter for describing the constitutive model, the evolution law of pore structure under the coupled T-H-M-C conditions, the scientific and reasonable index system reflecting the actual pore structure, and the prediction model for hydraulic characteristics based on the above index system.