Freezing-Thawing Hysteretic Behavior of Soils

The soil freezing characteristic curve (SFCC) plays a crucial role in investigating the soil freezing-thawing process. Due to the challenges associated with measuring the SFCC, there is a shortage of high-quality or rigorous test results with sufficient metadata to be effectively used for applications. Current researchers typically conduct freezing tests to measure the SFCC and assume a singular SFCC when studying the freezing-thawing process of soils, although limited studies indicated that there is a hysteresis during the freezing and thawing process. In this paper, a series of freezing-thawing tests were performed to assess the SFCC, utilizing a precise nuclear magnetic resonance apparatus. The test results reveal a hysteresis between the SFCC obtained from the freezing process and that from the thawing process. Through analyzing the test results, the hysteresis mechanism of the SFCC is attributed to supercooling. Supercooling inhibits initial pore ice formation during freezing, causing a drastic liquid water-ice phase change once supercooling ends. Despite being considered closely related, the hysteresis of the SFCC differs from the soil water characteristic curve (SWCC), and the models used to simulate the hysteresis of SWCC cannot directly be used. To address the impact of supercooling on soil freezing-thawing hysteresis, a novel theoretical model is proposed. Comparisons between the measured and predicted results affirm the validity of the proposed model. Understanding the freezing and thawing behavior of soils is critical for construction in cold regions. The soil freezing characteristic curve (SFCC), which describes the relationship between temperature and unfrozen water content, is essential for characterizing soil behavior during freeze-thaw cycles. However, measuring SFCCs for both freezing and thawing presents significant challenges, often resulting in simplifications and incomplete data in many studies. In this research, we conducted freezing-thawing tests using precise technology called nuclear magnetic resonance to examine the SFCC. We found a hysteresis between the SFCC during freezing and thawing, primarily attributed to supercooling, where the soil remains liquid below the freezing temperature. Supercooling delays initial ice formation, causing a rapid transition from liquid water to ice once it ceases. Importantly, the SFCC hysteresis differs significantly from the drying-wetting hysteresis in the soil water characteristic curve. To address this, we propose a novel model considering the impact of supercooling on soil freezing-thawing hysteresis. The proposed model fits well with the measured data and outperforms existing models. This study introduces a new understanding and a reliable model for soil freezing-thawing process, contributing to better comprehension of frozen soil phase changes. Supercooling is the primary cause of freezing-thawing hysteresis The hysteresis of the soil freezing characteristic curve differs substantively from that of the soil water characteristic curve The proposed model can address the impact of supercooling on soil freezing-thawing hysteresis