Preferential flow paths formation driven by hydrothermal interactions in the active layer of highway embankment in Inner Mongolia permafrost regions

Abstract

Preferential flow beneath highway embankments in permafrost regions plays a key role in accelerating permafrost degradation. However, the mechanisms driving its development under climate warming remain unclear, as hydrothermal interactions are believed to drive its evolution and compromise embankment stability. This study investigates hydrothermal dynamics within the active layer based on in situ experimentations of soil temperature and moisture collected from 2018 to 2023 along the Genhe–Labdalin Highway in the permafrost region of Inner Mongolia. The effects of climatic conditions and site-specific factors on hydrothermal dynamics and permafrost table variations are explored in detail. The main results are as follows: 1) The temperature and moisture in the embankment show periodical changes, and the moisture changes lag behind the temperature changes. The temperature and moisture fields of the embankment show lateral inhomogeneity, preferential flow paths appear underneath the embankment, and the internal moisture field of the embankment shows a concave shape. 2) The permafrost table of the embankment has been declining yearly. The asphalt pavement of the embankment and the wetland on the right side of the embankment, with the priority flow path underneath, accelerated the degradation of the permafrost, and the permafrost table of the embankment shows a concave shape. 3) Preferential flow paths of the embankment have a high capacity to transport moisture, accelerating the thawing of permafrost under the embankment for many years and severely affecting the stability and performance of the highway infrastructure. These findings reveal that preferential flow paths beneath highway embankments are closely linked to hydrothermal variations and are strongly influenced by freeze–thaw-induced soil structural changes. The formation and expansion of these flow paths significantly affect embankment stability. This study provides a theoretical basis for improving embankment design, construction, and long-term maintenance strategies in permafrost regions.