Frost Heave Evolution and Thermo-Hydro-Mechanical Coupling Analysis of Transmission Tower Foundations in Silty Clay of Seasonally Frozen Regions

Frost heave of transmission tower foundations in seasonally frozen regions endangers cold-region power infrastructure and grid security. This study establishes a coupled model to simulate foundation freeze-thaw and frost heave processes, validated via laboratory tests. The results demonstrate that the high thermal conductivity of the tower foundation alters the temperature field distribution, inducing preferential development of the freezing front along the foundation interface. During freezing, temperature gradients drive unfrozen water migration toward the freezing front, resulting in locally high-saturation zones in shallow soil after freeze-thaw. After freeze–thaw, plastic deformation of the soil and compression and rearrangement of soil particles degrade the uplift capacity of the tower foundation and prevent full recovery of its initial position, thereby producing residual displacement. Increases in the number of freeze–thaw cycles and initial water content both intensify the cumulative frost jacking effect on the tower foundation; moreover, soil with higher water content is more susceptible to consolidation settlement after thawing. The experimental data confirmed the reliability of the coupling model. These findings offer a theoretical foundation and numerical analysis methods for the long-term sustainable operation and maintenance of infrastructure in seasonally frozen regions.