Study on the Changing Pattern of the Salt-Freeze Swelling Force of Sulfate Saline Soil Containing Sodium Chloride Under Variable Temperature Environment

The salt-freeze swelling forces generated by sulfate saline soils when experiencing changes in ambient temperature can cause a large degree of damage to building foundations, endangering the safety of people's lives and property. We performed an experimental study on the change of salt-freeze swelling force under different conditions of salt content, cooling rate, and chlorine-sulfur ratio by using the self-developed salt-freeze swelling force test device in combination with the methods of indoor tests and mathematical statistics. The findings revealed that: The growth rate of the salt-freeze swelling force was positively correlated with the salt content. The salt-freeze swelling force of soils increased first and then decreased as the temperature decreased, and the maximum reduction reached 71.7%, which could be divided into three stages: rapid growth, slow growth, and fallback. The rate of temperature reduction had a significant impact on the deviation of the salt-freezing swelling force, and the two were positively correlated. The addition of sodium chloride could effectively inhibit the occurrence of salt-freeze swelling. Considering the economy and applicability, 0.3 is recommended to be considered as the chlorine-to-sulfur ratio in soils with CSR≥0.3; in soils with CSR<0.3, 0.3 and 0.1 are recommended to be considered for soils with high salt content (S>2%) and low salt content (S ≤ 2%), respectively. The final salt-freeze swelling force of sulfate-saline soils and sulfate-saline soils containing sodium chloride was predicted using a specific model, and its accuracy was confirmed by comparing it with previous studies.