高アルカリおよび海水系地下水を想定した溶液に浸漬したベントナイトを充填した人工亀裂を有する岩石の透水性

抄録

Following the closure of underground facilities at geological disposal sites, groundwater infiltration may result in swelling and gap-filling behavior of bentonite buffer material. This behavior likely aids the sealing of fractures of rock in excavation-damaged zones. However, the chemical composition of groundwater can influence this swelling and sealing behavior. As a result, the effectiveness of fracture sealing may vary, potentially leading to significant differences in host rock permeability. To evaluate the effectiveness of properties of rock as a natural barrier, it is essential to understand the extent to which it intrudes into rock fractures. Determining the permeability of the rock once these fractures are filled with bentonite is also crucial. This study entailed permeability tests on Horonobe mudstone and Mannari granite samples with artificially induced fractures. The fractures were filled with bentonite chemically altered by immersion in different solutions simulating potential chemical interactions in geological disposal environments. The experimental results indicate that fractures increase the permeability of the rock. However, permeability reduces when the fractures are sealed with bentonite. The extent of this reduction depends on the chemical composition of solution and type of rock.