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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.

Although a large number of previous researches have significantly contributed to the understanding of the quasi-static mechanical behavior of cemented tailings backfill, an evolutive porous medium used in underground mine cavities, very few efforts have been made to improve the knowledge on its response under sudden dynamic loading during the curing process. In fact, there is a great need for such information given that cemented backfill structures are often subjected to blast loadings due to mine exploitations. In this study, a coupled thermo-hydro-mechanical-chemical (THMC)-viscoplastic cap model is developed to describe the behavior of cementing mine backfill material under blast loading. A THMC model for cemented backfill is adopted to evaluate its behavior and evolution of its properties in curing processes with coupled thermal, hydraulic, mechanical and chemical factors. Then, the model is coupled to a Perzyna type of viscoplastic model with a modified smooth surface cap envelope and a variable bulk modulus, in order to reasonably capture the nonlinear and rate-dependent behaviors of the cemented tailings backfill under blast loading. All of the parameters required for the variable-modulus viscoplastic cap model were obtained by applying the THMC model to reproducing evolution of cemented paste backfill (CPB) properties in the curing process. Thus, the behavior of hydrating cemented backfill under high-rate impacts can be evaluated under any curing time of concern. The validation results of the proposed model indicate a good agreement between the experimental and the simulated results. The authors believe that the proposed model will contribute to a better understanding of the performance of hydrating cemented backfill under blasting, and also to practical risk management of backfill structures associated with such a dynamic condition.

Natural methane (CH4) oxidation that is carried out through the use of landfill covers (biocovers) is a promising method for reducing CH4 emissions from landfills. Previous studies on peat-based landfill covers have mainly focused on their biochemical properties (e.g. CH4 oxidation capacity). However, the utilization of peat as a cover material also requires a solid understanding of its geotechnical properties (thermal, hydraulic, and mechanical), which are critical to the performance of any biocover. Therefore, the objective of this context is to investigate and assess the geotechnical properties of peat-based cover materials (peat, peat–sand mixture), including compaction, consolidation, and hydraulic and thermal conductivities. The studied materials show high compressibility to the increase of vertical stress, with compression index (Cc) values ranging from 0.16 to 0.358. The compressibility is a function of sand content such that the peat–sand mixture (1:3) has the lowest Cc value. Both the thermal and hydraulic conductivities are functions of moisture content, dry density, and sand content. The hydraulic conductivity varies from 1.74 × 10−9 m/s to 7.35 × 10−9 m/s, and increases with the increase in sand content. The thermal conductivity of the studied samples varies between 0.54 W/(m K) and 1.41 W/(m K) and it increases with the increases in moisture and sand contents. Increases in sand content generally increase the mechanical behavior of peat-based covers; however, they also cause relatively high hydraulic and thermal conductivities which are not favored properties for biocovers.