Study on relationship between electrical conductivity and effective ion concentration in saline soils

Soil electrical conductivity is a key indicator for assessing water content and concentration in soil. Additionally, it plays a crucial role in identifying the development location of the frozen front, determining vulnerable areas in geotechnical engineering, and evaluating the noninvasive permeability coefficient. To enable dynamic monitoring of water, heat, and salt in cold-saline soil regions, a series of tests was conducted to examine the dependence of electrical conductivity on factors such as temperature, salt content, water content, and salt type. A 5TE soil moisture-temperature-conductivity sensor was used to measure the electrical conductivity of sodium chloride and sodium sulfate soils. he analyses of these two types of saline soils were carried out under varying water contents (16–28%), temperatures (-20 to 25 °C), and salt contents (0–2%). Based on a typical model of unfrozen water content, the variation in effective ion concentration with temperature was determined. The effective ion concentration was linked to conductivity through the shared variable of temperature, and an effective ion concentration model was developed. To enhance the model's accuracy, the effects of both salt type and crystallization were taken into account. The proposed model was validated using existing models and experimental data. Results show that the change in conductivity with temperature occurs in three distinct stages, with higher initial water content leading to a steeper slope of conductivity during the rapid phase transition stage. The relationship between effective ion concentration and conductivity was found to vary exponentially at both positive and negative temperatures.