Fundamental Mechanism and Practical Implications of Residual Stress in Rock

Although rock is an ancient building material, it is surprisingly complex with engineering behaviour that remains to be fully understood, in particular its engineering behaviour. The phenomenon of residual stress (RSt), a distribution of internally locked in stresses within a material's microstructure related to material formation, has been identified in many materials (e.g., steel) including rock. Although RSt has been observed in rock the phenomenon has not been quantified or included in rock behaviour models used for engineering analysis. RSt may have practical implications to fracture formation and displacement around excavations in highly stressed, massive rock formations. For high level projects, such as geological isolation of nuclear waste, the practical implications of RSt may be significant in predicting fracture formation around excavations, which can potentially influence contaminant transport. This research program will examine and quantify the RSt phenomenon and its implications to rock mechanics. A study will be conducted to examine RSt as a fundamental rock behaviour component. Because of the complexity of observing the micromechanical mechanisms directly, an integrated methodology will be used that will utilize carefully monitored laboratory experiments augmented with interpretation using micromechanical numerical modelling simulations. Damage (microcrack formation) will be induced (typically with thermal loading) in cylindrical drill core specimens and the response due to the release of RSt will be monitored. Similarly, RSt release due to drilling in a rock block specimen, augmented with thermally-induced damage, will also be monitored. To quantify RSt effects, sophisticated three-dimensional, micromechanical (rock grain-based) numerical modelling will be used to simulate the experiments. The effects of RSt will be quantified through reconciliation of observed experiment response with model simulated behaviour. The findings will be used to develop a rock mechanics model that includes the previously disregarded RSt behaviour component. The practical implications of RSt to rock engineering problems will then be explored in two research components: 1. The application of RSt to rock damage, core disking and implications to rock stability around underground excavations; and 2. The application of RSt to rock excavation boundary displacement. The findings of the research program will have implications in obtaining a more complete understanding of engineering behaviour of rock failure and displacement with implications to underground excavations in mining, civil engineering, and sustainable energy project. This research program will support the training of several HQP including one doctoral, two masters and five undergraduate students, and will include training in both a laboratory environment and the use of advanced numerical modelling which are both skills needed in academia and Canadian industry.