3D quantification of microcracks and porosity withrespect to brittle failure

Abstract

Understanding of the coupling of microstructural parameters to the mechanical deformation of rock requires a multiscale workflow which incorporates the impact of small scale heterogeneity including micropores and microcracks. Previous studies that identify these small features have been limited to 2D or, in 3D, to very small (2-3 mm) samples. We describe an x-ray contrast workflow to quantitatively map microporosity and microcrack networks at <1 micron scale in 3D within homogeneous and heterogeneous core material up to 5cm in diameter—across 4 orders of magnitude. This workflow has been applied to a standard reference material for rock mechanics studies (Carrara marble) as well as a rock sample from a porphyry Cu-Au deposit. In the Carrara marble sample, we map submicron scale porosity along grain boundaries in 3D and tracked damage at grain boundaries as well as grain cracking in response to thermal stress by heating samples to varying temperatures. Crack densities, grain boundary area and aperture are enumerated for up to 100,000 grains and calcite grain translations and rotations during thermal cracking can be visualised. In the porphyry Cu-Au samples high resolution imaging illustrates a complex network of connected micropores and microfractures. Deformation has also been mapped consequent to Brazil shear stress tests to illustrate the correlation between mechanical response and mineralogy, crack densities, crack morphology and distribution. This X-ray CT mapping particularly illustrates the impact local crack heterogeneity can have on the mechanical properties that determine the behavior of these rocks during caving, blasting and comminution. The results illustrate how high resolution X-ray CT imaging of deformation to the sub-micron scale will inform studies of the mechanical and hydraulic response at the laboratory scale and has the potential to enhance forward modelling of rock behavior during mining operations. Show more