Study on the evolution of the dielectric properties of artificially frozen sand under temperature variation

Detecting and determining the development of the frozen wall is a vital component of artificial freezing engineering. The electromagnetic parameters of frozen soil play a critical role in the fast and accurate identification using high-frequency electromagnetic waves. This study investigated the impacts of various factors on the dielectric properties of artificial frozen soil through laboratory experiments. The dielectric properties and evolutionary characteristics of sand were measured under different conditions, including temperature, probing frequency, initial moisture content, and salt content. The experimental results obtained characteristic curves of the relative dielectric constant of frozen sand in the frequency range of 300–2000 MHz under various conditions. Quantitative analysis was conducted to examine the differences in the dielectric properties of frozen sand. The analysis indicated that, under low-temperature and salt-free conditions, a reflection coefficient above 0.464 can be utilized to identify frozen/unfrozen sand. Furthermore, ground penetrating radar (GPR) is capable of effectively detecting and differentiating between salt-containing unfrozen soil and frozen soil. This study provides a solid theoretical framework for the quantitative identification of freezing front and frozen wall development. Additionally, the research findings have substantial theoretical implications for defect detection in frozen walls and the quantitative inversion of temperature fields in frozen soil.