Cross-Scale Investigation of the Shear Behavior of Frozen Alkaline Saline Soil–Structure Interfaces in Western Jilin

The soil freezing and salinization in the western part of Jilin Province can easily lead to the failure of the canal slope protection at the soil-structure interface. In order to reveal the mechanical response mechanism of the interface under the complex environment, this study takes the frozen alkaline saline soil-structure interface in western Jilin as the research object. Through indoor direct shear test, three-dimensional laser scanning microstructure observation and nuclear magnetic resonance test, the influence mechanism of initial water content and salt content on the shear characteristics of the interface is explored from the macro-fine-micro perspective. The results show that the peak shear strength of the interface increases with the increase of the initial water content. With the increase of NaHCO3 content, the peak shear strength of the interface decreases first and then increases, and the turning point corresponds to the critical salt content of 1.5%. The fine-micro mechanism reveals that the mechanical characteristics are derived from the water-salt phase transition competition mechanism of unfrozen water lubrication weakening and salt crystallization strengthening. The results of this paper can provide theoretical basis and engineering application reference for the stability analysis and safety assessment of soil-structure interface in saline soil area of western Jilin.