## 3 Results
### Microscopic Evolutionary Properties of Hipparion Laterite Under F-T Effect  
Figure 13 presents a total of 12 sets of SEM images of Hipparion laterite specimens with different initial moisture contents subjected to 0, 2, 6, and 10 F-T cycles at a normal stress of 200 kPa. The images were captured at an actual magnification of \(\times\)500. Figure 13: SEM images (\(\times\)500 magnification) of specimens subjected to varying numbers of F-T cycles. (**a–c**) Moisture contents of 16–24% under 0 F-T cycles; (**d–f**) moisture contents of 16–24% under 2 F-T cycles; (**g–i**) moisture contents of 16–24% under 6 F-T cycles; (**j–l**) moisture contents of 16–24% under 10 F-T cycles. Hipparion laterite specimens with a low moisture content (16% and 20%) in their unfrozen and thawed states exhibit a dense structure with high clay mineral content. Soil particles are primarily held together by the strong cementation of fine soil particles, such as clay and sand, mainly through face-to-face contact. In contrast, Hipparion laterite with a high moisture content (24%) exhibited a looser structure and higher pore content. In the early stage of F-T cycling, soil particles agglomerate into flakes and strips, with mineral fragments and fine particles adhering to the surface of coarse particles [78]. This weakens the intergranular bonds, leading to the formation of pores, microfissures, and an increase in pore diameter. As the F-T effect intensifies, the content of fine particles decreases and their bonding weakens, transitioning to a form of weak cementation. Simultaneously, the content of coarse particles increases, leading to larger intergranular spaces. The contact mode between particles shifts from face-to-face to point-to-point contact and edge-to-edge contact. This process is accompanied by a continuous increase in the number of pores and secondary microfissures. After 10 F-T cycles, the soil structure becomes severely degraded, with particles exhibiting a flocculated structure and a high degree of dispersion. No significant changes are observed in the intergranular space. To quantitatively analyze the microstructural changes induced by F-T cycles in Hipparion laterite specimens with different initial moisture contents, the 500\(\times\) magnification micrographs were ultimately selected for analysis after comparing the clarity, quality, and microstructural parameter information within the observation areas of SEM images at different magnification levels. The images were analyzed in RGB mode to define statistical ranges, and key measurement indices were selected, including the pore direction angle, pore circumference and area, average pore diameter, and pore fractal dimension. The data were analyzed in conjunction with previous research and theoretical models. The two-dimensional apparent porosity and pore size distribution of Hipparion laterite specimens subjected to varying initial moisture contents and F-T cycles were determined. Pore size was classified into four categories: large pores (D > 32 \(\upmu\)m), medium pores (32 \(\upmu\)m > D > 8 \(\upmu\)m), small pores (8 \(\upmu\)m > D > 2 \(\upmu\)m), and micropores (D < 2 \(\upmu\)m). As shown in Figure 14, with the number of F-T cycles increased, the microporous content of the specimens decreased, whereas the proportions of medium and small pores increased [35]. Although the macroporous content showed a slight upward trend, the overall change remained insignificant. Notably, specimens with a 24% moisture content exhibited a reduction in the percentage of small pores and had a higher total average pore size than specimens with a lower moisture content (16% and 24%). The apparent porosity increased with the number of F-T cycles, with a steeper slope for specimens with a higher initial moisture content [38; 53]. This trend suggests that a higher soil moisture content intensifies the deterioration caused by F-T cycles, emphasizing moisture content as a key factor influencing pore microstructure changes.