Macroscopic and mesoscopic comparative study of frozen loess under loading and unloading

This paper utilizes computed tomography (CT) real–time observation technology to investigate the damage mechanism of frozen loess under loading and unloading. The intrinsic connections between macroscopic mechanical degradation and mesoscopic damage in frozen loess were established through a comparative analysis of macroscopic mechanical parameters (such as dissipation energy and elastic strain energy) and mesoscopic structural parameters (such as porosity increment and mesoscopic structural damage increment) of frozen loess under loading and unloading. Furthermore, the relationships between damage variables at different scales under the effects of loading and unloading were explored. The experimental results demonstrate that during the elastic strain stage, the dissipated energy, porosity increment, and microscopic damage increment of frozen soil exhibit a linear increase with strain. Following loading and unloading, the porosity is unable to be fully restored to its original state due to the development of new cracks. At this stage, the deformation is not entirely elastic and includes some plastic deformation. During the plastic deformation stage, the dissipated energy tends to stabilize, while the porosity increment and microscopic damage increment continue to increase substantially. The pore structure of a specimen undergoes significant alterations, with increased displacement and rearrangement of soil particles and ongoing expansion of cracks. The damage evolution trends at both the macroscale and mesoscale remain consistent during this stage. This study offers insights into the construction of a cross–scale macroscale/mesoscale ontological damage model, serving as a valuable reference for future research.