Shear Strength of Compacted Bentonite Saturated with Saline Solutions under Different Specimen Saturation Methods
Publication: International Journal of Geomechanics
Volume 24, Issue 3
Abstract
The effect of saline on the shear strength of compacted bentonite is important to investigate the safety assessment of engineering barriers of deep geological repositories. Different methods used for saturating compacted specimens yield inconsistent relationships between shear strength and salt solution concentration. In this study, we performed direct shear tests on compacted Na–bentonite saturated with distilled water and Na solutions using the constant-vertical stress (CP) method and the constant-volume (CV) method. Scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) measurements were conducted to investigate the microstructural characteristics of compacted bentonite. The results show that the measured shear strength increases with increasing vertical stress or solution concentration. Furthermore, the shear strength of specimens prepared through the CV method is larger when distilled water is used for saturation; at the same time, when salt solutions are used for saturation, CP samples show greater shear strength. On the microscale, both SEM images and NMR results show that specimens become increasingly aggregated with increasing pore-water salinity and that saline solution has a greater effect on the microstructure of the compacted bentonite when using the CP method for saturation because of the change in volume during saturation. The intergranular stress equation, which considers physicochemical effects, is introduced to theoretically characterize the mechanical behavior of compacted bentonite. It is found that the relationship between intergranular stress and shear strength is unique, independent of the saturation method. In other words, the salt solution concentration affects the microstructure, thereby affecting the interparticle stress of compacted bentonite.
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Data Availability Statement
All data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request.
Acknowledgments
This work was supported by the Beijing Natural Science Foundation (Grant Number 8234058) and the Second Tibetan Plateau Scientific Expedition and Research Program (Grant Number 2019QZKK0905).
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International Journal of Geomechanics
Volume 24 • Issue 3 • March 2024
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© 2024 American Society of Civil Engineers.
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Received: Apr 10, 2023
Accepted: Sep 14, 2023
Published online: Jan 11, 2024
Published in print: Mar 1, 2024
Discussion open until: Jun 11, 2024
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