Hydrothermal Performance of Conventional Inclined and Base-Arranged Novel Horizontal Two-Phase Closed Thermosyphons in a Wide Asphalt Embankment Under Permafrost Warming

Climate warming, pavement heat storage and lateral heat intrusion accelerate active-layer deepening and uneven thaw settlement along permafrost transportation corridors. In wide asphalt embankments, heat is stored across a broad pavement-embankment section, while slope-aspect solar input drives asymmetric thermal erosion toward the sunny-side toe. Existing embankments protected by two-phase closed thermosyphons (TPCTs) are commonly evaluated by temperature reduction, maximum thaw depth or local cooling efficiency, but these metrics do not describe frozen-state continuity or residual weak zones. This study develops a three-dimensional hydrothermal model to compare a no-TPCT reference embankment, a conventional inclined TPCT layout and a base-arranged novel horizontal TPCT layout under long-term regional warming. Without TPCTs, the year-20 thaw depth reached 10.06 m at the sunny-side shoulder and 9.76 m beneath the centerline, with thermal disturbance propagating toward the sunny-side toe. Both TPCT layouts stabilized the 0 °C isotherm beneath the embankment. The inclined layout generated deep localized cooling, whereas the horizontal layout formed a more continuous shallow frozen zone, with longer operating durations and year-20 annual cumulative cooling capacities of 1870 and 1600 MJ on the sunny and shaded sides, respectively. The findings support an assessment based on frozen-state continuity, cross-sectional temperature uniformity and residual weak-zone development. Base-arranged novel horizontal TPCTs are better suited to shallow continuity, whereas inclined TPCTs remain useful for deep localized cooling.