Measuring and modeling the dielectric constant of soil during freezing and thawing processes: an application on silty clay

Accurately measuring the dielectric constant of soil and modeling it during freezing and thawing processes are important foundations of estimating the physical and chemical properties and moisture transfer characteristics of soil. In this study, a new test method was developed by combining five temperature probes and a 5TM sensor. Based on this method, a series of experiments for measuring the dielectric constant were conducted using silty clay as an example. The effects of freezing and thawing processes, water content, and salt on the dielectric constant of soil were comprehensively compared and analyzed. The results showed that the trends of soil dielectric constant as a function of temperature can be divided into a linear stage and a nonlinear stage. The soil dielectric constant measured during the freezing process was larger than that measured during the thawing process at the same negative temperature. However, the differences between them were related to the water content of the soil sample in the positive temperature range. In addition, the soil dielectric constant increased with the increase in water, NaCl, and K2SO4 contents, which was particularly major in the positive temperature range. Finally, a new empirical model was proposed to calculate the dielectric constant of soil. The verification results demonstrated that the calculated dielectric constants agreed well with the measured results. This work can provide references for the measurement and prediction of soil dielectric constant.