Study on Seasonal Permafrost Roadbed Deformation Based on Water–Heat Coupling Characteristics

The deformation and damage to seasonal permafrost roadbeds, as seasons shift, stems from the intricate interplay of temperature, moisture, and stress fields. Fundamentally, the frost heave and thaw-induced settlement of soil represent a multi-physics coupling phenomenon, where various physical processes interact and influence each other. In this investigation, a comprehensive co-coupling numerical simulation of both the temperature and moisture fields was successfully executed, utilizing the secondary development module within the finite element software, COMSOL Multiphysics 6.0. This simulation inverted the classical freezing–thawing experiment involving a soil column under constant temperature conditions, yielding simulation results that were in excellent agreement with the experimental outcomes, with an error of no more than 10%. Accordingly, the temperature, ice content, and liquid water content distributions within the seasonal permafrost region were derived. These parameters were then incorporated into the stress field analysis to explore the intricate coupling between the moisture and temperature fields with the displacement field. Subsequently, the frost heave and thaw settlement deformations of the roadbed were calculated, accounting for seasonal variations, thereby gaining insights into their dynamic behavior. The research results show that during the process of freezing and thawing, water migrates from the frozen zone towards the unfrozen zone, with the maximum migration amount reaching 20% of the water content, culminating in its accumulation at the interface separating the two. Following multiple freeze–thaw cycles, this study reveals that the maximum extent of freezing within the roadbed reaches 2.5 m, while the road shoulder experiences a maximum freezing depth of 2 m. A continuous trend of heightened frost heave and thaw settlement deformation of the roadbed is observed in response to temperature fluctuations, leading to the uneven deformation of the road surface. Specifically, the maximum frost heave measured was 51 mm, while the maximum thaw settlement amounted to 13 mm.