Study on the Impact Dynamics and Fracture Morphology of Cement-Improved Aeolian Sand Under Freeze–Thaw Cycles

Cement-improved aeolian sand is a potentially sustainable geomaterial that has been used in engineering applications such as subgrade filling and slope stabilization in cold regions. To investigate the degradation patterns of the dynamic mechanical properties of improved aeolian sand following freeze–thaw cycles, this study conducted the Split Hopkinson Pressure Bar (SHPB) test on cement-improved aeolian sand under different freeze–thaw cycle numbers and cement content, revealing its dynamic mechanical characteristics, energy dissipation patterns, and failure mechanisms. The results indicate that, as the number of freeze–thaw cycles increased, internal microcracks progressively develop and propagate, and the dynamic mechanical properties of the modified soil gradually deteriorate. This is manifested by a gradual decrease in the dynamic peak stress, a decline in the dissipated energy density, and an upward trend in the fractal dimension of the fragment mass. Compared to the deterioration observed during the first ten freeze–thaw cycles, the magnitude of the changes in dynamic mechanical parameters decreased, indicating a gradual reduction in the overall rate of deterioration. The addition of cement enhances the frost resistance of the modified soil; however, an excessively high cement content shifted the failure mode toward brittle fracture. and the fractal dimension exhibits a decreasing trend. The conclusions of this study offer a theoretical framework for catastrophe mitigation in cement-improved aeolian sand, including freeze–thaw and dynamic loading.