# Effects of Freeze-thaw Cycles on the Mechanical Properties and Microstructure of a Dispersed Soil
## 3 Result and Discussion
### UCS Test  
The freeze-thaw cycles have a substantial impact on the mechanical behavior of soils, mainly attributed to the interconnected relationship between water, ice, and soil [34]. Figure 7 depicts the stress-strain behavior of the soil samples following freeze-thaw cycle testing. The stress-strain curves reveal notable differences when comparing the unfrozen soil sample, which exhibits significant peaks indicating a strain-softening behavior and brittle damage, with the curve obtained after a freeze-thaw cycle. In the latter case, the stress-strain plot exhibits a noticeable decline, characterized by a gradual reduction in the peak magnitude. Subsequent to attaining the peak, the axial strain further increases, accompanied by a gradual attenuation in the rate of axial stress reduction. This transition from strain softening, observed in the 0 freeze-thaw cycle, to strain hardening indicates plastic failure of the soil samples. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Number of F–T Cycles**} & **Mass of \textless{5} \(\upmu\) Soil Particles Using** & **Mass of \textless{5} \(\upmu\) Soil Particles** & \multirow{2}{*}{**Dispersion (\%)**} \\  & **Unconventional Methods (g)** & **Using Conventional Methods (g)** & \\ \hline
0 & 23.20 & 26.31 & 88.18 \\
1 & 28.76 & 30.92 & 93.02 \\
3 & 32.50 & 33.40 & 97.31 \\
5 & 31.86 & 33.42 & 95.34 \\
7 & 31.82 & 33.08 & 96.19 \\
9 & 29.74 & 30.92 & 96.19 \\
12 & 30.40 & 34.95 & 86.98 \\
15 & 33.21 & 36.41 & 91.21 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Sample results of double hydrometer tests. Figure 6: Variations in soil dispersion with different numbers of freeze-thaw cycles. The highest point value on each curve in Figure 7 represents each soil sample's unconfined compressive strength (qu). Separate variation curves were plotted for qu and SDP to facilitate the analysis of their behavior at each freeze-thaw stage (Figure 8a,b). As depicted in Figure 8a, the unconfined compressive strength (qu) significantly decreases after the first freeze-thaw cycle, and following the initial freeze-thaw cycle, it can be divided into three distinct stages based on varying reduction percentages. The first stage encompasses one to five freeze-thaw processes, during which the reduction in qu remains relatively consistent, with an average decrease of approximately 40%. The second stage occurs after seven to nine freeze-thaw cycles, where the qu value after the seventh cycle decreases compared to that after the fifth cycle, indicating the initiation of the second stage. At this stage, the reduction in qu remains relatively constant, with an average decrease of around 50%. By the 12 th cycle, the decreasing trend starts to slow down, although the reduction continues. It can be assumed that the impact of structural damage on qu in the soil samples diminishes a higher number of freeze-thaw cycles during the third stage. The relationship between SDP and the number of freeze-thaw cycles is illustrated in Figure 8b. The change in SDP can also be roughly divided into three stages. After the first freeze-thaw cycle, SDP remains stable after 1-5 freeze-thaw cycles, followed by a significant increase after 7-9 freeze-thaw cycles, and finally stabilizes after 12 freeze-thaw cycles. The variations in SDP indicate that the strength loss caused by the freeze-thaw action is more pronounced in the first two stages. In contrast, the degree of strength deterioration gradually diminishes with an increase in freeze-thaw cycles. SDP shows slow growth with an increasing number of freeze-thaw cycles and eventually stabilizes before reaching 15 freeze-thaw cycles. Therefore, it is crucial to study the irreversible damage occurring in soils within the first ten freeze-thaw cycles. Figure 8: Effect of freeze–thaw cycles on the UCS test: (**a**) the qu of soil and (**b**) the SDP of soil. Figure 7: Stress–strain curves of dispersed soil subjected to varying freeze–thaw cycles.