https://orcid.org/0000-0001-7388-7501
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Abstract
A geological repository has been considered as one of the best options for the disposal of high-level radioactive waste (HLW), with the concepts of an engineered barrier system (EBS) and a natural barrier system. A compacted bentonite buffer is the most crucial component of the EBS. Because groundwater penetrates the compacted bentonite buffer, it is essential to investigate a water-retention curve (WRC) of the compacted bentonite buffer to evaluate the overall safety performance of the EBS because the WRC of the compacted bentonite buffer can affect the thermal-hydraulic–mechanical behavior of every component of the EBS. Therefore, this technical note reports on laboratory experiments conducted to analyze the WRC for a Korean Ca-type compacted bentonite considering dry density, confined or unconfined condition, and drying or wetting path. Models by Fredlund and Xing and by van Genuchten had the best fit with the experimental data. The results revealed higher water content with smaller dry density and in an unconfined condition and higher total suction during the drying path. Furthermore, the air-entry values (AEVs) and fitting parameters of the van Genuchten model were compared with other Ca-type bentonites produced in Europe. A smaller AEV showed lower expansibility since the AEV is affected in the low-suction range and expansibility.
Nomenclature
| a = | = | fitting parameter for WRC |
| M = | = | molecular mass of water |
| m = | = | fitting parameter for WRC |
| n = | = | fitting parameter for WRC |
| P = | = | vapor pressure of air |
| po = | = | saturated vapor pressure of specimen |
| PvG = | = | fitting parameter for van Genuchten model (MPa) |
| R = | = | gas constant [8.31 J/(mol K)] |
| T = | = | temperature (K) |
Greek
| α = | = | fitting parameter for van Genuchten model (MPa−1) |
| θ = | = | volumetric water content |
| θr = | = | residual volumetric water content |
| θs = | = | saturated volumetric water content |
| λ = | = | pore-size distribution index |
| λvG = | = | fitting parameter for van Genuchten model |
| ρd = | = | dry density (g/cm3) |
| Ψ = | = | water potential (MPa) |
| Ψb = | = | air-entry value (MPa) |
Acknowledgments
This research was supported by the Nuclear Research and Development Program of the National Research Foundation of Korea (NRF-2017M2A8A5014857) and by a grant (18CTAP-C143742-01) from the Technology Advancement Research Program funded by the Ministry of Land, Infrastructure and Transport of the Korean government.