Laboratory Strength Testing of Argillaceous Limestone Under Varying Saturation, Scale, Loading Rate, and Confinement Conditions

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Jaczkowski, Eric
Cobourg Limestone , Crack Initiation , Crack Damage , Uniaxial Compressive Strength , Brazilian Tensile Strength , Triaxial Strength , Saturation Effect , Scale Effect , Loading Rate Effect , Confinement Dependency , Experimental Testing Methodology
The Deep Geological Repository (DGR) concept is the proposed solution for the long-term storage of nuclear waste in Canada. While site selection processes are currently underway for high-level waste storage, a low and intermediate waste storage DGR is planned for development at depth in Kincardine, Ontario. The DGR site is to be hosted in the Cobourg limestone, a rock formation which presents varying heterogeneity at different scales. The successful design of long-term nuclear waste storage requires engineered barriers and geology designed to safely and securely contain contaminants. The excavation of hard rocks at depth can induce damage to the surrounding rock mass. This damage corresponds to the initiation and propagation of fractures and is related to in situ stress conditions and excavation processes. Heterogeneous rock masses can further complicate the initiation and propagation of fractures, causing inconsistent behaviour related to the variability of the rock. The changing in situ conditions of DGR host rocks can also influence fracture behaviour, highlighting the need for a better understanding of the effect of rock conditions on the damage behaviour of brittle rocks. This research examines the influences of various testing conditions on the geomechanical properties of Cobourg limestone, to address the changing in situ conditions that may be present during long-term storage of nuclear waste. The effects of specimen saturation, scale, loading rate, and confinement have been investigated through the laboratory strength testing of specimens representative of Cobourg limestone found at depth for the proposed low and intermediate level DGR site. Using standardized laboratory testing practices and newly developed experimental methodologies, this thesis describes the influences of testing condition on the elastic and strength properties of the rock. The testing methodology is presented and examined to evaluate the effectiveness of the different testing conditions in properly characterizing the Cobourg limestone. The observations and results from this work provide details regarding the physical properties and failure behaviour of the rock, as well as non-standard testing techniques for investigating heterogeneous rock masses. This research provides insight into the characterization of brittle rock failure under different testing conditions, which is important for future DGR site selection.
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