Assessing the influence of microstructural features on deformation of rocks under triaxial loading

Abstract

Assessing the influence of microstructural features on the deformation of rocks under triaxial loading is vital in rock engineering applications, aiding safe and efficient operations by predicting the deformation of rocks. Triaxial testing offers the simulation of stress conditions within a rock to examine the deformation of rocks with confinements. This research focuses on how microstructural features, such as cementing material and pore geometry, affect the deformation behaviour of rocks subjected to triaxial loading. Two rock types were considered in this study: Kimachi sandstone (medium hard clastic rock) and Bibai sandstone (hard clastic rock). The progressive failure behaviour under Hydro Mechanical (HM) coupling effect was analysed by stress-strain distribution and the fracture geometry was examined using CT images of the specimens which were tested under different confinements. Thin sections were analysed to examine the changes in porosity and the effect on the cementing material with the confinement. The results of the proposed approach reveal a clear influence of the effective confinement on the failure of rocks and how it influences the porosity and cementing material of rocks. It is found that the Bibai sandstone shows a brittle failure and a shearing deformation while Kimachi sandstone shows a brittle to ductile failure and shearing to compaction deformation with the confinement due to the less presence of cementing material within Bibai sandstone compared to Kimachi sandstone. Therefore, with the confinement, the porosity of Bibai sandstone increases while it decreases in Kimachi sandstone. The results highlight the differences in the failure mechanism of a particular rock type for the same effective confinement which is a result of only a partial contribution of the pore pressure on the failure. These findings provide valuable insight into the assessment of microstructural features on the deformation of rocks under triaxial loading, aiding in the development of safer and more efficient rock engineering operations.