In-situ monitoring reveals the energy regulation mechanism of two-phase closed thermosyphons in wide asphalt highway embankments in high-altitude permafrost regions

The bearing capacity and stability of permafrost engineering are fundamentally governed by the ground thermal regime. In high-altitude regions, the coupling of intense solar radiation and the high heat absorption of wide asphalt pavements exposes embankments to severe energy input, exacerbating permafrost degradation. Consequently, two-phase closed thermosyphons (TPCTs) have been adopted as efficient cooling measures. However, a systematic understanding of TPCT energy regulation mechanisms, cross-seasonal cold transport, and long-term cumulative effects in wide, high-heat-absorbing embankments remains lacking. To address this gap, this study analyzes the energy regulation and cold migration characteristics of TPCTs based on in-situ monitoring. Results indicate that TPCTs effectively mitigate warming, maintaining the permafrost table nearly identical to the natural state, with a difference of only 0.1−0.2 m. The effective cooling period spans mid-October to mid-April, creating a significant cooling zone at 4−8 m depth with an influence radius of 2.5 m and reducing ground temperatures by 2−3 °C. Although TPCTs cease operation during the warm season, the embankment retains a low-temperature advantage, keeping soil temperatures at 3−9 m more than 0.7 °C lower than natural ground by the season's end. Furthermore, TPCTs exhibit a continuous inter-annual cumulative cooling effect, characterized by a decrease in deep permafrost temperature of 0.01−0.02 °C/a and a permafrost table rise of 0.02 m/a. These findings confirm that TPCTs effectively inhibit permafrost degradation and enhance embankment thermal stability, providing a scientific basis for the design and construction of wide highways in high-altitude permafrost regions.