Thermal and hydrological processes in permafrost slope wetlands affect thermosyphon embankment stability

Abstract

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 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 °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.