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UBC Theses and Dissertations

Impact of pore fluid chemistry on mechanical and thermal behavior of clay-based materials Tabiatnejad, Bardia


The impact of pore fluid salinity on thermal and mechanical properties of clay-based materials are examined in this thesis. The proposed concept for deep geological repository in Canada consists of a series of clay-based material to support the used-fuel bundles in place and minimize the local groundwater infiltration, which is highly saline. The coupled process of local groundwater infiltration and thermal desiccation in the engineered barrier causes the material to experience unsaturated conditions with increased salt content levels. In the previous studies, the behavior of the material has been investigated in the distilled water conditions, which was necessary to consider the change in the pore fluid salinity considering the infiltration of the groundwater. This research investigates the impact of the pore fluid salinity on the mechanical behavior and thermal conductivity of the clay-based materials which are designed to be use in the repository in future. To accomplish this, three experimental testing programs have been carried out. The first experimental program examined the shrinkage and stress-strain behavior of bentonite-sand buffer specimens prepared with high and low salt concentrations. The results were compared to the available data from the literature for the specimens prepared with distilled water. Specimens were dried out in desiccators and installed in triaxial cells. The soil water characteristic, compression and shear strength of the specimens were presented and impact of the pore fluid salinity was discussed. The second experimental program evaluated the effect salinity of the pore fluid on the behavior of the light backfill material in unsaturated conditions. Specimens prepared with distilled water and saline solution were tested and their compressibility and shear strength were discussed. The third experimental program investigated the impact of pore fluid salinity on the thermal conductivity of mixtures of bentonite and silica sand at low and high dry densities. In continue, a number of thermal conductivity prediction models were selected to calculate the thermal conductivity values of the material with distilled water and saline pore fluids. The calculated values were compared to the obtained experimental data and a suitable model for predicting thermal conductivity in the saline pore fluid condition was presented.

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