JRMGE / Vol 14 / Issue 3
Swelling ability and behaviour of bentonite-based materials for deep repository engineered barrier systems: Influence of physical, chemical and thermal factors
Mohammed Alzamel, Mamadou Fall, Sada Haruna
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Department of Civil Engineering, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada
2022, 14(3): 689-702. doi:10.1016/j.jrmge.2021.11.009
Received: 2021-03-24 / Revised: 2021-11-05 / Accepted: 2021-11-21 / Available online: 2022-03-23
2022, 14(3): 689-702.
doi:10.1016/j.jrmge.2021.11.009
Received: 2021-03-24
Revised: 2021-11-05
Accepted: 2021-11-21
Available online: 2022-03-23
Compacted bentonite–sand (B/S) mixtures have been used as a barrier material in engineered barrier systems (EBSs) of deep geological repositories (DGR) to store nuclear wastes. This study investigates the individual and combined effects of different chemical compositions of deep groundwaters (chemical factor) at potential repository sites in Canada (the Trenton and Guelph regions in Ontario), heat generated in DGRs (thermal factor), dry densities and mass ratios of bentonite and sand mixtures (physical factors) on the swelling behavior and ability of bentonite-based materials. In this study, swelling tests are conducted on B/S mixtures with different B/S mix ratios (20/80 to 70/30), compacted at different dry densities (ρd = 1.6–2 g/cm3), saturated with different types of water (distilled water and simulated deep groundwater of Trenton and Guelph) and exposed to different temperatures (20 °C–80 °C). Moreover, scanning electron microscopy (SEM) analyses, mercury intrusion porosimetry (MIP) tests and X-ray diffractometry (XRD) analyses are carried out to evaluate the morphological, microstructural and mineralogical characteristics of the B/S mixtures. The test results indicate that the swelling potential of the B/S mixtures is significantly affected by these physical and chemical factors as well as the combined effects of the chemical and thermal factors. A significant decrease in the swelling capacity is observed when the B/S materials are exposed to the aforementioned groundwaters. A large decrease in the swelling capacity is observed for higher bentonite content in the mixtures. Moreover, higher temperatures intensify the chemically-induced reduction of the swelling capacity of the B/S barrier materials. This decrease in the swelling capacity is caused by the chemical and/or microstructural changes of the materials. The results from this research will help engineers to design and build EBSs for DGRs with similar groundwater and thermal conditions.
Keywords: Deep geological repository, Engineered barrier, Bentonite-sand materials, Nuclear waste, Swelling capacity, Swelling strain
Article Data
Author(s) Information
Prof. Mamadou Fall
mfall@uottawa.ca
Dr. Mamadou Fall is a Full Professor in the Department of Civil Engineering at the University of Ottawa (Canada), the Chair of the Department of Civil Engineering and the Vice President Technical of the Canadian Geotechnical Society. He graduated from the Earth Science Institute at the University of Dakar (Senegal) and was awarded a PhD excellence scholarship for his PhD studies in Germany. Subsequently, he was granted a postdoctoral fellowship by the German Research Foundation and coordinated the German Research Chair of Environmental Geosciences and Geotechnics. Prof. Fall and his team are performing leading-edge research in the geotechnical and geoenvironmental fields in close collaboration with the industry, major federal and provincial governmental institutions, and international partners. He has been leading several major research projects that are related to geotechnical hazards and risks, mine waste management, underground disposal of nuclear wastes, landslides, problem grounds, coupled thermo-hydro-mechanical-chemical (THMC) processes in geosystems and transportation geotechnics. He is currently supervising a large research team of postdoctoral researchers and graduate students (PhD and Master). He is included in the World's Top 2% Scientists list, published by Stanford University and Elsevier in 2021.