As a new type of subgrade fill

steel slag-stabilized soil was characterized by high heterogeneity and discontinuity. It is difficult to directly study the microscopic characteristics of its failure mechanism through traditional mechanical testing and theoretical analysis methods. In order to reveal the damage mechanism of steel slag-stabilized soil

uniaxial compression tests were conducted combined with a real-time X-ray computed tomography (CT) test

and the dynamic evolution characteristics of microscopic cracks under four typical strain levels were analyzed based on image processing and three-dimensional visualization. The results show that the steel slag-stabilized soil experienced four stages

including initial compaction

elastic deformation

plastic yield and residual deformation. A localized shear band appeared in the middle of the specimen in uniaxial compression process. The two-dimensional porosity and dispersion degree of crack distribution continuously improved with the increasing axial strain. Three-dimensional reconstruction models vividly revealed that the cracks experienced three development stages

including initial germination

rapid expansion and stable state. Three-dimensional porosity and crack connectivity are exponential function and linear function respectively with axial strain. The pore size distributions show that the primary cracks gradually expand and penetrate through the entire specimen and contribute to a main fracture that leads to the structural damage. Thus

the expansion and connection of cracks are the internal reasons of strength softening and instability failure of specimen under uniaxial loading. The uniaxial compression-CT real-time scanning results can effectively reveal the damage evolution characteristics of materials. The research results provide a new perspective for understanding the failure mechanism of soils and have important reference for promoting the application of industrial waste slag in geotechnical engineering.