Effects of NaCl concentration on thermal conductivity of clay with cooling

Abstract

The thermal conductivity of soils is a key factor in calculating soil heat transfer and analyzing the temperature fields in geotechnical engineering projects in cold regions. In this study, investigations have been carried out with respect to the effect of temperature (T), concentration of sodium chloride (C), and water content (w) on the thermal conductivity of clay soil. A series model is applied to develop a new theoretical equation that relates thermal conductivity to the water content and temperature. In addition, ultrasonic testing is used to determine the volume of unfrozen water in frozen soil. The results show that the freezing temperatures of samples with an NaCl salt concentration of 0%, 2%, and 5% are − 2 °C, − 4 °C, and − 8 °C respectively. The theoretical equation can explain the relationship between the thermal conductivity and temperature and water content of frozen soil. There is an exponential function for the relationship between thermal conductivity and temperature of clay samples at temperatures below freezing. There is a small reduction in the thermal conductivity of the salt-free samples due to the propagation of frost heave cracks from − 6 to − 10 °C. An increase in the electrolyte concentration of the solution would compress the electrical double layer, thus leading to the increase in contact between the surface of the soil particles. When the salt concentration is increased to 5%, flocculation occurs between clay particles. There is a quadratic function for the relationship between thermal conductivity and NaCl concentration of clay soil. The thermal conductivity of the salt-free samples increases with higher water content at temperatures above freezing and decreases with higher water content due to the propagation of frost heave cracks when the samples are frozen. The generalized relationships between thermal conductivity and NaCl concentration and temperature can be used to evaluate the thermal conductivity in frozen saline soil.