Abstract
Anisotropic shrinkage of compacted bentonite blocks threatens the security of a buffer barrier in a geological disposal project for high-level radioactive wastes (HLW). In this investigation, fan-shaped buffer blocks on an industrial scale were compacted and exposed to an indoor environment to dry naturally. Digital image correlation (DIC) was used in an attempt to monitor the blocks’ shrinkage deformation in a vertical (z) direction, and dial indicators were used to measure horizontal (r and θ) shrinkage for comparison. Before and after the blocks desiccation, pore size distributions were investigated by mercury intrusion porosimetry (MIP) to analyze the shrinkage behavior in the microstructure, and the micro-fissuring was investigated by X-ray computed tomography (CT) in terms of internal visual structure. The initial evaporation stage on the industrial scale and over compaction of the blocks was not detected. In horizontal directions, isotropic shrinkage strains were observed, which were lesser than 2%. Linear shrinkage strains decreased with the increase of the initial lengths of the measuring lines, indicating that block shrinkage is mainly concentrated on the external part, while the internal part shows poorer shrinkage ability. CT images showed that no obviously micro-fissuring was found in a block before drying it and MIP results demonstrated that both macrostructure and microstructure at a 5 cm depth slightly changed after block desiccation. Vertical shrinkage, monitored by DIC, exhibited a poorer ability compared to the horizontal direction, which had almost equal linear strains though its initial measuring lines lengths were shorter. In future research, more attention should be paid to the lateral shrinkage of buffer blocks.
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Acknowledgments
The authors are grateful to the National Nature Science Foundation of China (41672261) and Fundamental Research Funds for the Central Universities (lzujbky-2017-ct02) for their financial support.
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Zhang, H., Tan, Y., He, D., Luo, G. (2019). Laboratory Investigation of Anisotropic Shrinkage of HLW Buffer Block: An Attempt Using Digital Image Correlation Method. In: Zhan, L., Chen, Y., Bouazza, A. (eds) Proceedings of the 8th International Congress on Environmental Geotechnics Volume 2. ICEG 2018. Environmental Science and Engineering(). Springer, Singapore. https://doi.org/10.1007/978-981-13-2224-2_61
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DOI: https://doi.org/10.1007/978-981-13-2224-2_61
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