Investigation of mesostructural changes in bimsoil during triaxial deformation: an insight using X-ray computed tomography and ultrasonic measurement

Abstract

In this paper, mesoscopic structural changes and the associated strain localization behaviors were investigated quantitatively using X-ray computerized tomography (CT) and ultrasonic measurement techniques. While the effects of rock blocks on the macroscopic mechanical of block-in-matrix soil (bimsoil) have been widely studied, the physical mesoscale mechanisms governing the bimsoil deformation are still poorly understood. Triaxial compression experiment was conducted on bimsoil sample with rock proportion of 30% (mass ratio). The mesostructural changes were quantitatively studied using macroscopic stress-strain description and mesoscopic CT image identification. Under triaxial compression, the stress-strain curve of bimsoil presents strain hardening behavior, and the interactions between rock block and soil matrix result in the strain localization and mesostructural changes. In addition, the damage evolution behaviors of bimsoil are different from soil and rock, and spatial kinematic of rock blocks results in not only the fluctuation of CT value, ultrasonic pulse velocity (UPV), and transmitted ratio (TR) but also the crack geometry characteristics (e.g., length, area, width, and fractal dimension). What is more, contaction and separation between soil matrix and rock block occur repeatedly during sample deformation, and the fractal dimension of the crack distribution becomes larger. Through a series of mesostructural change analysis, the mesomechanisms of bimsoil under triaxial deformation have been first discussed.