Dynamic Evolution of Cracks in Slag-Modified Soil under Uniaxial Loading Using Real-Time X-Ray Computed Tomography

Abstract

The cracking behavior of subgrade filling is crucial for the stability of road embankments. Slag-modified soil (SMS), which is commonly used as a reinforcing material for construction in highway and railway engineering, has special mechanical and microstructural characteristics that are easily altered under external disturbances. Although the macroscopic deformation of SMS has been widely examined, research on its cracking behavior at the mesoscale under an external load has received insufficient attention thus far. This study uses real-time X-ray computed tomography (X-CT) as a nondestructive tool for characterizing the microstructure of a SMS specimen subjected to uniaxial compression. Rules for the dynamic propagation of cracks in the specimen during deformation are identified based on two-dimensional (2D) and three-dimensional (3D) visualization and quantitative characterization. The results showed that the SMS can be divided into three components—cracks, soil, and steel slag—based on the density gradients from X-ray CT images. The preprocessed X-ray CT images and reconstructed crack models dynamically demonstrated the expanding and connecting patterns of internal cracks during the entire process of deformation. Values of the crack ratio and the degree of connectivity were positively correlated with the axial strain as expressed by a cubic spline function and a linear function, respectively. Curves of the distribution of the volumes of the cracks suggest that cracks in SMS can be divided into four groups: minicracks, mesocracks, medium cracks, and macroscopic cracks. From quantitative and visual perspectives, a large number of original cracks with small volume and low connectivity were gradually transformed into a main fracture under uniaxial loading. The localized shear band, which existed in the zone adjacent to the main fracture, was generated and obliquely distributed in an irregular, flat strip shape in the middle of the SMS specimen. This study suggests that the real-time X-ray CT scanning technique has broad application prospects for detecting the mesostructure in subgrade filling.