Characterization of orthotropic nature of cleavage planes in granitic rock

Abstract

Granite naturally exhibits anisotropic elasticity because of the alignment of minerals formed in the three orthogonal cleavage planes known as rift, grain, and hardway planes. Of critical importance for studying cleavage planes is to understand how they affect the spatial distribution of anisotropy. Here we use multiple approaches which measure tensile strength, ultrasonic wave velocity, and three-dimensional (3D) X-ray computed tomography (CT) imaging to elucidate the existence of cleavage. Our results show that essential features of cleavage-induced anisotropy, e.g., orientation of the failure mode and directional dependency of elastic constants, can be identified with high precision. Furthermore, the results highlight that the proposed CT image technique can achieve 3D spatial mapping of anisotropy, providing a causal link between the cleavage planes and the spatial distribution of anisotropy in granite. This comprehensive understanding through the described techniques could have practical uses in predicting the fracture path and potential flow pathways for petroleum, groundwater, natural gas, etc.