Abstract
Due to its low hydraulic conductivity, high swelling capacity, and good adsorption properties, the Gaomiaozi (GMZ) bentonite has been selected as potential buffer/backfill materials for construction of engineered barriers in the deep geological repository for disposal of high-level nuclear waste (HLW) in China. Investigation of salt solution effects on the water retention properties of compacted bentonite is of great importance in the context of geological disposal of HLW based on the multibarrier concept. In this study, amended specimens were obtained through a spray of different concentrations of salt solutions to reach target salt contents, respectively. With employment of the vapor phase technique for suction control, water retention tests were conducted on densely compacted GMZ bentonite (1.7 Mg/m3) with different salt contents under confined conditions. Corresponding soil water retention curves (SWRCs) were obtained. Analysis indicates that, for a given suction, the measured water content of GMZ bentonite specimen increases as the salt content (or pore fluid concentration) increases. The influencing rate depends on suction. For lower suctions (lower than 38 MPa), the water retention capacity increases as the salt content increases, while for higher suctions (higher than 38 MPa), the influence can be negligible. Based on the Fredlund and Xing (1994) equation, a soil water retention model was proposed for simulation of the SWRCs of compacted GMZ bentonite with consideration of pore fluid chemistry. Parameters were analyzed and determined with consideration of influences of the pore fluid concentration. Verification indicates that the SWRCs simulated by the proposed model are well agreed with the measured ones.
Highlights
Compacted bentonite has been recommended as a buffer/backfill material in many countries for engineered barriers in the deep geological repository for disposing high-level nuclear waste (HLW) [1,2,3,4,5,6,7,8,9]
For lower suctions, water retention capacity increases with the increase in salt content, while for higher suctions, the influence was negligible
This phenomenon was faded as the suction increased, which may attribute to the decrease in water content
Summary
Compacted bentonite has been recommended as a buffer/backfill material in many countries for engineered barriers in the deep geological repository for disposing high-level nuclear waste (HLW) [1,2,3,4,5,6,7,8,9]. The compacted bentonite will undergo a complex—highly coupled thermal (T), hydro (H), mechanical (M), and chemical (C)—process during the long-term operation of a repository [10,11,12], i.e., simultaneous heating from decay of nuclear waste in the canister, infiltration of groundwater from the surrounding geological formations, possible leakage of nuclides from the canister, and swelling pressure of bentonite on hydration To assess these coupled processes of the engineered barrier system, a number of investigations have been conducted [1, 3, 9, 13,14,15] and related modeling approaches [16,17,18] have been proposed. For compacted bentonite, modified water retention models were developed with consideration of temperature and dry density effects [31, 32] These equations are composed of two or three fitting parameters, which are evaluated by using either laboratory results at different moisture contents or statistical relationships between the suction and other basic soil properties. A modified soil water retention model for the compacted GMZ bentonite with consideration of salt solution concentration effects was established and verified
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