The solid waste soda residue (SR) exhibits a high content of soluble salts, and the liquid phase soluble salts in soda residue soil (SRS) undergo phase transition crystallization during cooling process, leading to subgrade salt expansion and deformation damage. In order to explore the salt mechanisms of SRS, this paper systematically analyzes the impact of SR content on the salinization and salt expansion characteristics of SRS using soluble salt tests and salt expansion experiments. Combined with X-ray diffractometry (XRD) and low-temperature frost shrink tests, the study analyzed the salt expansion process of SRS. The results indicate that under different SR content, SRS is classified as chloride saline soil. The SRS is categorized into weak saline soil, moderate saline soil, strong saline soil, and over-saline soil with different soda residue dosage. During cooling from 20 degrees C to -25 degrees C, all SRS groups exhibit initial salt expansion followed by frost shrink deformation characteristics. As the SR content increases within the 0 % - 40 % range, the temperature range for severe salt expansion gradually decreases from 5 degrees C to -15 degrees C. At 25% SR content, SRS exhibits the most severe salt expansion, while excessively high SR content inhibits the crystallization of sulfate salt phase transitions. The study identifies three stages in the salt expansion process of SRS: promotion stage, severe stage, and inhibition stage. The research findings provide valuable insights for the prevention of salt expansion in SRS and the widespread utilization of SR in road applications.

To broaden the sources of earthwork and the utilization of soda residue (SR) and fly ash (FA), SR, FA, and clay were mixed to form a soda-residue soil (SRS) by adding externally moderate content of lime or/and cement for further stabilization. Through the orthogonal scheme, 9 groups of proportions were designed. Subsequently, the unconfined compressive strength (UCS) at different curing ages was conducted. Afterward, the stress-strain pattern, the UCS and water absorption, the sensitivity of factors and levels to UCS, and the deformation modulus were analyzed. Finally, the enhancement mechanism of SRS from physicochemical reactions was explored by analyzing gradation and microstructure. The results show that the patterns of stress-strain curves on SRS at different curing ages are similar; all have obvious stress peaks, and the specimens of SRS present a brittle failure. With the extension of curing ages, the UCS of all proportions increased; the UCS of the G2 group increased the most, reaching 85.44%, and the G9 group increased the least, only 1.92%. However, the water absorption quality decreased, and G6 decreased the most (37.53%), G7 decreased the least (0.84%), and UCS and water absorption quality showed a negative correlation. The sensitivity of each factor to UCS was different; the SR was the most sensitive at 7 d, but the lime was the most sensitive at 28 d. The sensitivity of each factor level (content) to UCS remains unchanged at different curing ages. There is a linear relationship between the deformation modulus and UCS. The analysis demonstrates that the better strength properties of SRS are mainly determined by the superior gradation and the reaction of materials.