Study on the coupling mechanism of water-heat-vapor-salt-mechanics in unsaturated freezing sulfate saline soil

Understanding the internal regularity of unsaturated freezing sulfate saline soil is of utmost importance concerning the durability and stability of cold region engineering in sulfate saline soil areas. One-sided freezing experiments were performed on unsaturated sulfate saline soils with varying salt and moisture contents and temperature gradients to investigate the interplay of water-vapor-salt migration, heat transfer, ice-water and water-vapor phase transformations, salt crystallization, and salt-frost heave. This study presented a novel water-heat-vapor-salt-mechanics coupling model that considers water-vapor-salt migration and its feedback on soil deformation. The results signify that the water accumulation at the top surface of unsaturated freezing sulfate saline soil is primarily due to water vapor migration. Water-vapor-salt migration, ice-water phase transition, and salt crystallization form more ice and salt crystals, filling the air-filled pores and causing significant salt-frost heave. Water vapor transfer and accumulation further exacerbate the soil deformation for unsaturated freezing sulfate saline soil. The calculating results agree with the test data and demonstrate the efficacy of the proposed five-field coupling model. These findings hold significant implications for developing practical solutions for mitigating the negative impacts of salt-frost heave induced by water-vapor-salt transfer in unsaturated freezing sulfate saline soil on construction projects.