## 3 Results and Analysis
### Compaction Characteristics and Pore Size Distribution
#### 3.1.3 Freeze-Thaw Cycles' Effects on Soils with Different Compaction Degrees
The curve of the void ratio vs. the number of freeze-thaw cycles is shown in Figure 13. It can be seen that the void ratio of the compacted sample increased with the number of freeze-thaw cycles, indicating that the freeze-thaw cycles increased the pore volume in the soil, in accordance with previous research results [43, 44, 45]. According to Figure 12; Figure 13, the freeze-thaw cycles had the same effect on the differently compacted soils. When N\({}_{\text{FT}}\) < 4, there was a slight change in void ratio, which then gradually increased with further freeze-thaw cycles. Freeze-thaw cycles caused the proportion of micropores to decrease, while the mesopores increased. It is worth noting that the void ratio of dense soil increased more. After 12 freeze-thaw cycles, the void ratios of the soils with 100% and 90% compaction degrees increased by 27.5% and 18.3% in an obvious manner. This agrees with [PERSON] [46], who reported that the void ratio of a lime, fly ash and loess mixture increased by about 14% after 10 freeze-thaw cycles. The possible reason is that in the  
Figure 11: Pore size distribution curves for soils with different freeze–thaw cycles. Figure 12: Relationship between the proportion of the peak area ratio and freeze–thaw cycles. Figure 10: \(T_{2}\) time distribution curves for soils with different freeze–thaw cycles. negative-temperature environment, the water in the pores of saturated soil varies from liquid to solid, thereby causing a change in pore structure and increase in void ratio. If the frost-heaving force is greater than the force between the particles, the expansion of the pores is promoted. [PERSON] et al. [44] make the same point. [PERSON] et al. also believed that the change in particle structure would stop when the frost-heaving force and transfer force were less than the structural strength of the soil. After four freeze-thaw cycles, sub peak 1 of the dense soil began to increase significantly, while the loose soil showed a more gradual change. The difference in the internal pore structure (moisture content, soil structure and pore water distribution) of soils with different compaction degrees caused the macroscale deformation behavior to perform differently faced with freeze-thaw cycles. Compared with loose soil, the soil particles of the dense sample were closely arranged; there was a smaller void ratio and pore size, contributing to the stability of the soil. At the beginning of the freeze-thaw cycles, the adjustment of the pore size distribution was small; with an increase in the number of cycles, the repeated phase change of water in the pores caused the soil pores to increase in number and size. There was space for the adjustment of the soil particles when the soil was loose. As a result, in the early freeze-thaw cycles, the pore size distribution varied, while the void ratio remained constant. However, further freeze-thaw cycles would cause an increased void ratio. When the cycles reached a certain number, the structure of the dense soil gradually approached that of the loose soil, and eventually, the void ratios of the soils with different compaction degrees became closer. Increasing the number of freeze-thaw cycles may lead to the same void ratios for both sample types.