## 1 Introduction
Under the assumption of geometric symmetry, [PERSON] et al. [19] proposed a more accurate prediction method for SWCCs based on the analysis of the SWCC shape features of S, C-1 and C-2 critical points. Compared with the SWCC obtained from experiments, it is shown that the improved prediction method can effectively reduce the deviation of direct-fitting-empirical equations for finite-class soil data. [PERSON] et al. [20] proposed a formula for determining the SWCC characteristic parameters, and discussed the relationship between the SWCC characteristic parameters and the fitting parameters of the model from [PERSON] et al. [10] and [PERSON] [10] for calculation and analysis, which aimed at replacing the traditional graphic method and providing consistent results. [PERSON] proposed a sample size scale effect coefficient to predict AEVs [21]. There are also some researchers [22; 23; 24; 25] who used a variety of statistical mathematical methods to evaluate and modify the accuracy of the proposed prediction model. A better estimate of the SWCC is called upon to require more accurate consideration of soil types, properties, and water temperature states in nature. Owing to the fact that the engineering project is actually affected by natural factors (e.g., moisture fluctuation and climate variation), many researchers have devoted themselves to the study of suction changes in the wet and dry paths, as well as different temperature states, and the causes of such changes in recent years. [PERSON] et al. [26] examined the error of in situ soil estimation using a SWCC without considering the wet and dry effect, and gave a median and suction range that could estimate the in situ soil suction. His estimation results showed that the error of estimating suction clay of in situ soil by a SWCC was higher than that of sandy soil. [PERSON] et al. [27] studied the hysteresis in the growth and dewetting of five types of sandy soils. The results showed that the lower dry density and coarser soil particles would result in lower intake and residual values. [PERSON] et al. [28] used the phenomenological method to model the lag SWCC in any dry and wet path. Between 5 \({}^{\circ}\)C and 35 \({}^{\circ}\)C, soil-suction tests at different temperature gradients showed that temperature had little effect on soil suction. For the arid and semi-arid seasonal permafrost regions, the freezing and thawing process would cause various structural changes inside the subgrade soil, which seriously affected the strength and soil characteristics of the subgrade [29; 30; 31]. Some studies need to be continued, for example, by establishing a general prediction model suitable for various types of soil freezing and thawing characteristics, so that the F-T characteristics of the required soil samples could be quickly obtained in the absence of data. In order to explore the changes of the soil-water characteristic curve after the F-T cycles, this study is aims the development of unsaturated low-liquid-limit silty clay in seasonally frozen soil areas. The matric suction of three different dry densities was measured by the filter-paper method, and the change in suction of the soil was tested after zero, one, three, five, and seven F-T cycles. The change in pores produced by F-T cycles of different cycles was analyzed by an SEM, and the changes in suction caused by F-T of the soil were analyzed.