The Influence of Mineralogy and Grain Scale Features in Healed Intrablock Structure on Direct Shear Properties in the Cobourg Limestone

The role of sedimentary nodular intrablock structure in the Cobourg limestone on rockmass behaviour is an important consideration for the Bruce site Canadian Deep Geological Repository for nuclear waste storage that requires detailed geomechanical laboratory testing and the application of sophisticated numerical tools for long-term behaviour prediction. It is therefore critical to determine appropriate geomechanical properties of the host rock. The Cobourg limestone is found near surface in the Bowmanville quarry, which provides access to samples for direct shear and other geomechanical laboratory test programs. It is essential to develop correlations between the properties of the Cobourg limestone from the Bowmanville to Bruce sample source locations. This study presents a detailed mineralogy investigation to determine the composition of the Cobourg limestone at both locations using X-Ray Diffraction, Scanning Electron Microscopy, and Mineral Liberation Analysis. The results are used to explain trends in laboratory direct shear test stiffness and strength properties of the Cobourg limestone from the Bowmanville and Bruce sites.