Water and salt migration characterization in NaHCO3 saline soils during unidirectional freezing conditions

In cold regions, the eutectic action of the NaHCO3-H2O binary system during the freezing process affects the migration of water and salt in NaHCO3 saline soils. This study aims to investigate the migration of water and salt in open and closed systems, utilizing unidirectional freezing tests with different salt contents. By considering the phase diagram of pore solution and phase transition theory, two phase-change paths can be observed in NaHCO3 saline soils during freezing. These paths result in different migration patterns for water and salt, depending on the salt and water content conditions of the samples. The theoretical and experimental results both validate that water migrates from the unfrozen zone towards the eutectic action and ice crystallization zone during the freezing process. Under low-salinity conditions, salt migrates from the ice crystallization zone towards the eutectic action and unfrozen zone. Conversely, under high-salinity conditions, salt migrates from the unfrozen zone towards the eutectic action. Moreover, it is observed that a high salt content hinders water migration.