# Effects of Freeze-thaw Cycles on the Mechanical Properties and Microstructure of a Dispersed Soil
## 4 Conclusions  
This study explored the correlation between the mechanical strength of soil and freeze-thaw cycles in a seasonal permafrost region. The geotechnical properties of the tested soil samples were comprehensively investigated, considering factors such as particle size composition, microscopic characteristics, and dispersion. The mechanism of soil deterioration under freeze-thaw conditions was determined by analyzing the experimental results. Drawing upon the acquired findings and subsequent discussions, the following conclusions can be inferred:  
1. The dispersibility of the soil samples progressively increases with an increasing number of freeze-thaw cycles. Simultaneously, the corresponding increase in dispersion negatively affects the soil's mechanical strength. Overall, these two variables exhibit a negative correlation. Figure 16: Illustrative diagram illustrating the transformation of soil particles under freeze–thaw conditions. 2. With an increasing number of freeze-thaw cycles, the particle size distribution of the soil samples exhibits a general trend of fragmentation of large particles and gradual accumulation of smaller particles. The sand content decreases from 38.76% to 16.59%, and the clay content increases from 7.48% to 24.20%. 3. During the first nine freeze-thaw cycles, the reduction in strength is significant, with the unconfined compressive strength decreasing from 156.843 kPa to 76.961 kPa. After nine freeze-thaw cycles, the rate of decrease in strength slows down, and the unconfined compressive strength stabilizes at around 70 kPa. Furthermore, the c-value gradually decreases from 22.196 kPa in the unfrozen state to 7.997 kPa and then stabilizes. The \(\varphi\)-value starts at 7.514\({}^{\circ}\) in the unfrozen state, peaks at 9.514\({}^{\circ}\), and gradually declines. 4. With increasing freeze-thaw cycles, new cracks continuously form, existing cracks expand, and the surface porosity increases from 14.47% in the unfrozen state to 32.10% after the 15 th freeze-thaw cycle. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app13179849/s1](https://www.mdpi.com/article/10.3390/app13179849/s1)]([https://www.mdpi.com/article/10.3390/app13179849/s1](https://www.mdpi.com/article/10.3390/app13179849/s1)). Figure S1: Relationship curves between vertical deformation and shear displacement in direct shear tests of tested soil samples after different numbers of freeze-thaw cycles (where F-T n represents the number of freeze-thaw cycles); Table S1: Summary of Final Results. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app](https://www.mdpi.com/article/10.3390/app)]([https://www.mdpi.com/article/10.3390/app](https://www.mdpi.com/article/10.3390/app))  
* [PERSON] et al. (2015) [PERSON]; [PERSON]; [PERSON] Examination of the Physico-Chemical Composition of Dispersive Soils. _Period. Polytech._**2015**, _60_, 269-279. [CrossRef]
* [PERSON] et al. (2020) [PERSON]; [PERSON]; [PERSON] Effect of Cations and Anions on Flocculation of Dispersive Clayey Soils. _Heliyon_**2020**, \(6\), e03462. [CrossRef] [PubMed]
* [PERSON] (1980) [PERSON] Freezing Phenomena in Soils--ScienceDirect. _Appl. Soil Phys._**1980**, _16_, 254-299. [CrossRef]
* [PERSON] (1984) [PERSON]; [PERSON] Creep and Strength Testing of Frozen Saline Fine-Grained Soils. _Can. Geotech. J._**1984**, _21_, 518-529. [CrossRef]
* [PERSON] and [PERSON] (1993) [PERSON]; [PERSON] Creep Behavior of Saline Fine-Grained Frozen Soil. _J. Cold Reg. Eng._**1993**, \(7\), 77-89. [CrossRef]
* [PERSON] (1994) [PERSON] Influence of Chemical Compositions of Salts on Strength and Deformability of Frozen Saline Soils. _Osn. Fundam. I Mekhanika Gruntov_**1994**, \(6\), 18-22. * [PERSON] and [PERSON] (2011) [PERSON]; [PERSON] Strength of Frozen Saline Silt under Triaxial Compression with High Strain Rate. _Soil Mech. Found. Eng._**2011**, _48_, 196-202. [CrossRef]
* [PERSON] et al.