Heating method shows considerable potential for mitigating frost heave of subgrade in cold regions. However, the water-heat-deformation characteristics of subgrade under the coupling effect of freezing-thawing and heating effect remain unclear, which hampers the optimization and widespread application of heating method. Therefore, this paper proposes a numerical model of subgrade water-heat-deformation considering heating effect. The influence and mechanism of heating effect on water-heat-deformation of subgrade is systematically analyzed. The results show that the heating effect changes the water-heat-deformation state of subgrade. Furthermore, the combined influence of shady-sunny slope effect and ballast layer ensures that ground temperature near the subgrade center remains above 0 degrees C, thereby preventing the formation of ice lenses and frost heave. However, the shoulders on both sides enter a freezing state, and freezing rate, freezing depth and frost heave are reduced by more than 45 %, 60 % and 60 % respectively compared with the comparison subgrade. The freezing depth, driving force and rate of water migration are significantly affected by heating effect, which increases the pathways of water upward migration and greatly weakens the segregated frost heave of subgrade. This is the primary mechanism through which the heating method effectively mitigates frost heave in subgrades.

The long-term stability of the cast-in-place footings in permafrost regions has received much attention due to its climate sensitivity. The current research lacks long-term data validation, especially in the context of climate change. Based on the 13-year (2011-2023) temperature and deformation monitoring data from the Qinghai-Tibet Power Transmission Line, this study investigates the characteristics of permafrost variation and its impact on the stability of tower footings under the cooling effect from thermosyphons. The results reveal that the thermosyphons effectively reduce the ground temperature around the footings. After the first freeze-thaw cycle, the soil around the tower footings completed refreezing and maintained a frozen state. In the following 13 years, the ground temperature continued to decrease due to the cooling effect of thermosyphons. The duration notably exceeded the previously predicted 5 years. The temperature reduction at the base of the footings corresponded well with the frost jacking of the tower footings and could be divided into three distinct phases. In phase 1, the ground temperature around the footings rapidly reduced, approaching that of the natural field, while the footings experienced pronounced deformation. In phase 2, the ground temperature decreased at a faster rate, and the deformation rate of the footings slowed down. In phase 3, the frost jacking of the footings gradually retarded with the decrease in base temperature. Additionally, the ground temperature differences of over 1 degrees C were observed among different tower footings, which may lead to the differential deformation among the tower footings. The ground temperature differentiation is attributed to the difference in solar radiation intensity, which is shaded by the tower structure from different directions. This study provides theoretical support and empirical accumulation for the construction and maintenance of tower footings in permafrost regions.

To ensure the long-term service performance of infrastructure such as railways, highways, airports and oil pipelines built on permafrost slope wetland sites, it is imperative to systematically uncover the long-term heat-water - water changes of soil in slope wetlands environment under climate warming. More specifically, considering valuable field data from 2001 to 2019, the long-term heat and water changes in active layers of the slope wetland site along the Qinghai- Xizang Railway (QXR) are illustrated, the effect of thermosyphon measures in protecting the permafrost environment is evaluated, and the influences of climate warming and hydrological effects on the stability of slope wetland embankments are systematically discussed. The permafrost at the slope wetland site is rapidly degrading, demonstrating a reduction in active layer thickness of > 3.7 cm per year and a permafrost temperature warming of > 0.006 degrees C per year. The thermosiphon embankment developed by QXR has a specific cooling period; thus, to mitigate the long-term impacts of climate warming on the thermal stability of permafrost foundation, it is essential to implement strengthening measures for the thermosiphon embankment, such as adding a crushed-rock layer or sunshade board on the slope of thermosiphon embankment to creating a composite cooling embankment. Short-term seasonal groundwater seepage intensifies frost damage to the slope wetland embankment, while long-term seasonal supra-permafrost water and groundwater seepage exacerbates uneven transverse deformation of slope wetland embankment. Long-term climate warming and slope effects have altered the surface water and groundwater hydrological processes of slope wetlands, potentially leading to an increased occurrence of slope embankment instability. These results are crucial for improving our understanding of heat and water variation processes in the active layer of slope wetland sites located in permafrost regions and ensuring long-term service safety for the QXR.