Using X-ray computed tomography to investigate the effect of confining pressure on meso-structural changes and crack damage evolution in soil and rock mixture during triaxial deformation

Abstract

This article aims to quantitatively investigate the influence of confining pressure on the mesoscopic structural changes using X-ray computerised tomography (CT) for soil and rock mixture (SRM). While the effects of confining pressure on the macroscopic mechanical characteristics have been widely studied, the physical meso-mechanisms governing the SRM deformation are still poorly understood. A triaxial compression experiment was conducted in SRM samples with a rock block proportion of 30%, under confining pressures of 60, 120 and 200 kPa, respectively. The meso-structural changes were quantitatively studied using a macroscopic stress–strain description and mesoscopic CT image identification. Under triaxial deformation, the stress–strain curves present strain hardening behaviour, and the strength of the sample increases with the increase of confining pressure. In addition, the crack distribution is extremely non-uniform and strongly affected by the existing rock blocks. The crack scale presents a reduction trend with increasing confining pressure. What is more, the most striking observation from the CT images is that cracks may disappear during deformation owing to the interactions between the soil matrix and rock blocks. Through a series of meso-structural evolution analysis, the meso-mechanisms of the effect of confining pressure on SRM under triaxial deformation have been presented first.