Use of X-ray computed tomography to investigate the effect of rock blocks on meso-structural changes in soil-rock mixture under triaxial deformation

Construction and building of engineering structures in geomaterials with soil and rock mixture (SRM) are often challenging tasks for engineers. While the effects of rock block content on the macroscopic mechanical properties have been widely studied, the physical meso-scale mechanisms governing the SRM deformation are still poorly understood. Here, we applied a high energy X-ray Computed Tomography (CT) imaging method to study the influence of rock block content on the mesoscopic structural changes and the associated strain localization behaviors in SRM. Triaxial compression experiment was conducted for the SRM samples with rock block percentage (RBP) of 0%, 30%, 40%, and 50%, respectively, under a confining pressure of 120 kPa. The meso-structural changes were quantitatively studied using the macroscopic stress-strain descriptions and mesoscopic CT images identification. Under triaxial deformation, the stress-strain curves present strain hardening behavior, strength of the sample increases with increasing RBP, which can be verified from the interlocking of rock blocks, and skeleton role of blocks improves the capacity to resist deformation. In addition, regions of localization are extremely non-uniform and strongly affected by the rock blocks, scale of the localized bands presents a incremental trend as RBP increases. What is more, the most striking observation from the reconstructed images is that zone of localization may disappear during deformation owing to the interactions between the rock block and soil matrix. Through a series of meso-structural evolution analysis, the meso-mechanisms of the effect of rock block content on SRM under triaxial deformation have been documented.