Moisture migration inference and calculation along the muddy clay column under unidirectional freezing based on LF-NMR

During the process of excavating underground space by artificial ground freezing (AGF), moisture migration can aggravate the freeze-thaw destruction of the soil, which will lead to the destruction of the overlying surface and adjacent buildings. Currently, unfrozen water content is often used as an important manifestation of moisture migration within the soil. Therefore, determining the amount of unfrozen water in a timely manner is significant to investigate the characteristics of moisture migration on artificial frozen soils and enhance the reliability of buildings. In this study, moisture migration in large muddy clay columns is characterized by low-field nuclear magnetic resonance (LF-NMR), and the unfrozen water content at different moments is obtained. Moreover, the changes of unfrozen water content in the column are further calculated by the segregation potential (SP) model and LF-NMR experimental data derivation, respectively, according to the position of the freezing front during freezing. Results demonstrate that the variation of unfrozen water content with time is closely associated with the position of the freezing front, which significantly affects the unfrozen water content in some scanning layers. Furthermore, using the SP theory and NMR data derivation, the amount of water migration within the column under freezing is obtained. Meanwhile, the applicability of SP theory in describing moisture migration in closed systems is indirectly demonstrated, and the calculated value of the amount of moisture migration is 94.27% of the maximum moisture migration deduced using NMR data. Finally, the microscopic analysis of moisture migration is conducted by combining the quantitative calculation of the amount of moisture migration and the evolution of the freezing front. This study can provide a reference for calculating the amount of water migration within the soil during freezing using SP theory, and can help the safe construction of cold areas or artificial freezing projects.