## 1 Introduction
Therefore, the environmental durability of S/S-contaminated soil is extremely sensitive to environmental changes. The impact of F-T cycles on S/S HM-contaminated soil will continue to be focused on in-depth in this study. Freeze-thaw cycles mainly occur in seasonal frozen regions. The moisture in the soil constantly transforms between liquid and solid with the periodic change of temperature: through changes in the volume of water in different fractions, as well as the free migration of water, the pore structure and density of the soil are changed, which is one of the direct factors affecting the migration effect of HMs. In China, the area of seasonal permafrost is about 5.14 million square kilometers, accounting for 53 percent of the total land area [37]. According to the second national soil erosion remote sensing survey, China's F-T erosion area has reached 13.4% of the country's total area [38]. Because of the vast F-T area, it is of great practical significance to explore the influence of the F-T cycle on the S/S of HM-contaminated soil. After 12 F-T cycles, the leaching concentrations of Pb/Zn-contaminated soil and composite Zn-Pb-contaminated soil increased greatly [34]. The elastic modulus of silty clay and modified clay can be significantly reduced after four F-T cycles [39]. After conducting seven F-T cycles on silty clay, [PERSON] et al. concluded that the number of F-T cycles had a great influence on the mechanical properties of soil [40]. Studies have confirmed that under the long-term effect of simple F-T cycles (180 cycles, 180 days), the unconfined compressive strength loss rate of cemented contaminated soil can reach more than 30%, and the concentration of HM ions in HM leaching solution can increase by more than 20% [18; 41; 42]. This research has been improved on this basis, and \"long-term\" is the keyword of this. Studying the condition of HMs in the soil during the long F-T cycle period, observing the S/S effect of the HMs is a good way to ensure the long-term use of the S/S soil. Effective control of HMs in soil under adverse conditions is of great significance to prevent secondary pollution of HMs. A maximum of 90 F-T cycles (90 days) was set up under the same F-T mode to explore the stability of HMs under long-term F-T cycles in this research. After making up for the problem of short-term F-T, the situation of HMs in the soil has also been improved, and the transformation from single HM pollution to compound HM pollution research has been realized. According to a large number of studies, one source of pollution often produces multiple types of HM pollution [41; 42; 43]. As, Cd, Cr, Cu, Mn, Ni, Pb, Zn, and other HMs exist in the farmland soil of the Qixia mining area in Nanjing, China [44]. There are many HMs in the weathered coal gauge, and the surrounding land is also harmed by HMs such as Zn, Cd, and Cr. Research on a single HM-contaminated soil can no longer meet the actual needs. Therefore, in this study, three pollutants, Pb, Zn, and Cd, were added to the soil at the same time. The adsorption-desorption, precipitation reaction, complexation reaction, and oxidation-reduction reaction between HMs and soil allow HMs to exist in different forms in soil, and different forms of HMs exhibit different toxicity and environmental behavior [45]. When HMs are in a less bioavailable form or a more stable form, their risk in the environment is low. Therefore, the content of each form of HMs can be used as an observation indicator to assess the risk of HMs in soil. The improved Tessier method was used to extract seven fractions of HMs in the soil in this study. Based on the above analysis, the improved Tessier method was adopted to detect the content of various forms of HMs (Pb, Zn, and Cd) in the soil that had undergone six F-T cycle conditions (0, 3, 7, 14, 30, and 90 cycles) up to 90 days, and the functional groups were analyzed by Fourier transform infrared spectroscopy analysis tests.