The correlation between phase transition and electrochemical characteristics of composite saline soil

The phase transition characteristics of saline soil are closely related to its electrochemical processes. It is an effective means to investigate the phase transition mechanism by using the electrochemical characteristics of saline soil. In order to explore the electrochemical characteristics of composite saline soil in phase transition process, the electrochemical impedance spectrum of saline soils with different mass ratios of chloride and sulfate ions were tested through cooling tests. The results reveal that Nyquist plots exhibit a single reactance arc at positive temperatures, and the water/salt migration in the soil changes the electrochemical reaction process after the pore water freezing, resulting in the appearance of diffusion impedance. The impedance modulus increases linearly with the decrease in temperature before phase transition, while the formation of salt crystals and ice crystals leads to a significant increase in the impedance modulus after phase transition. The phase angle is close to zero degrees at a scanning frequency of 10⁵ Hz, indicating that the soil system exhibits resistive behavior. Moreover, the equivalent circuit model is established according to the conductive path of the composite saline soil. It was found that there is a close correlation between the value of equivalent resistance elements and the impedance modulus through comparison. In addition, the machine learning algorithms were used to predict the variation of equivalent resistance elements, which demonstrate that the XGBoost model can effectively predict the variation of resistance value, with an R² of 0.995. This research provides a theoretical reference for studying the salt expansion and frost heave mechanism of saline soil in cold regions.