Abstract: The deformation of foundation soil caused by freeze-thaw cycles is a typical geological disaster in engineering construction in permafrost areas. Fiber optic sensing technology provides an important technical means for accurate and distributed real-time monitoring of frozen soil deformation. To explore the feasibility of distributed fiber optic strain sensing in monitoring frozen soil deformation, this study utilized a self-developed optical cable-frozen soil interface mechanical characteristics tester to investigate the failure mechanism of the cable-soil interface in frozen soil samples with different dry densities and initial water contents. The experimental results indicate that the fiber optic strain monitoring results accurately reflect the progressive failure characteristics of the cable-soil interface, and the strain softening model can better describe the mechanical properties of the interface. During the freezing process, the liquid water in the soil becomes ice, causing the movement of the freezing front and water migration, and resulting in significant differences in the mechanical properties of the interface. The evolution process of the shear stress at the cable-soil interface at different depths reflects the deformation coordination state with the frozen soil during the cable pullout process, indicating that the measurement range of the cable and the coupling of the interface are closely related to the dry density and initial water content of the soil. This study provides a reference for the application of optical fiber sensing technology in deformation monitoring of frozen soil foundation in cold regions.

Key words: geotechnical engineering monitoring, frost heave effect, fiber optic cable-frozen soil interface, progressive failure, distributed fiber optic sensing technology