## 4 Discussion  
Under the action of surface runoff and underground seepage, the crystalline salts inside a saline soil are dissolved to form a salt solution and become lost in water. This process weakens the cementation ability between soil particles and increases the porosity of the soil, thus leading to a decrease in the stability of the overall soil structure. On this basis, when the saline soil is subjected to self-weight and external load, the soil particles break the  
Figure 8: Precipitation of sodium sulfate crystals from the surface of treated sulfate saline soil after curing for 14 days: (**a**) Content of CLI is 0%; (**b**) Content of CLI is 4%; (**c**) Content of CLI is 8%; (**d**) Content of CLI is 12%. Figure 7: Changes in the moisture content of samples and mass of barium sulfate in samples with different CLI contents and curing times: (**a**) moisture content of samples; (**b**) mass of barium sulfate in samples. original stable structure and reorganize, which easily induces a series of geological disasters such as soil subsidence and collapse. Therefore, the changes in the mechanical properties and the soluble salt content of the study samples are discussed to further elucidate the action mechanism of polymer active agents on saline soil. The effect and mechanism for improving a sulfate saline soil are shown in Figure 9. Dry soil was mixed with the appropriate amount of water and CLI to obtain the desired specimens. For the unmodified plain soil (0% CLI content), a thick hydration film existed on the surface of the soil particles with a large number of connected pores between the particles. The molecular structural formula of CLI is shown in Figure 9a, which is weakly acidic due to the hydroxyl and sulfonic groups and chelates with calcium ions, providing strong stability. In water, soil, and ion (sodium and calcium ions are provided by anhydrous sodium sulfate and polymer active agent, respectively) environments, the weakly acidic CLI makes the pH lower, i.e., hydroxyl ion decreases, leading to a decrease in the net negative charge number on the particle surface and a thinner double electric layer. Meanwhile, the high-valence calcium ions provided by CLI experience an ion-exchange reaction with sodium on the surface of the soil particles (Figure 9a). It is known that when the surface charge of clay particles is constant, ion valence increases with the ion concentration and decreases with the thickness of the double layer of soil particles according to the theory of a double layer of soil. Therefore, the double layer thickness of the modified soil particles decreases, leading to an increase in the attraction between the particles, which in turn produces an agglomeration effect to achieve the effect of compacting the soil. Additionally, as an anionic polymer, the sulfonic group of CLI is negatively charged in an aqueous environment, which can be adsorbed onto the surface of soil particles under the effect of cation bridging and binding the cations in situ. Due to the characteristics of macromolecular groups, CLI forms a spatial network structure between neighboring soil particles, which plays a strong bonding effect. As shown in Figure 9b, at the optimal doping content, CLI filled the intergranular pores, and it wrapped and bonded the soil particles. It also induced the formation of the agglomerated flocculated structure of soil particles, which decreased the specific surface area of the soil body, and the mechanical properties of the modified soil were optimal. However, CLI preferentially binds to itself to form macromolecules as the content continues to increase since the chelating property is good. Some of the sulfonic groups are bonded to the neighboring sulfonic groups of CLI by hydrogen bonds (Figure 6a). This is not as significant as cation bridging, resulting in a decrease in the friction force between the soil particles. As shown in Figure 9b, an excessive CLI matrix increases the distance between soil particles, making compaction of the soil difficult and thus exposing more voids.