Thermal performance and heat transfer process of an expressway embankment with horizontal-thermosyphons in permafrost regions

Two-phase closed thermosyphon (TPCT) has been considered to be an effective measure to reduce soil temperatures and maintain engineering stabilities in permafrost, but deformations and cracks of a testing expressway with inclined insertion thermosyphon embankment (ITE) were found to be serious and aggravated year by year. Monitoring results from 2011 to 2018 indicate that uneven temperatures and permafrost thawing are main causes for the disease in ITE. To address this issue, a horizontal insertion thermosyphon embankment (HTE) was proposed in this paper. Numerical results show that thermal performance of HTE is much better than that of ITE. In October of the 20th service year, base temperatures of HTE at center, sunny and shady foot can be reduced to −2.3 °C, −1.2 °C and − 1.6 °C, respectively. Low-temperature (≤ − 1 °C) contours in HTE showed a layered and nearly symmetric distribution, covering almost the entire base width range. The width of −1.5 °C isotherm can be increased by 61%, and the estimated annual heat release of deep soils can be increased by 72% compared with ITE. The thermal enhancement of HTE is because the horizontal-thermosyphon doubles the contact surface with soils and heat dissipation, and effectively reduces the heat flux difference. The horizontal-thermosyphon could be considered for application in expressways built on permafrost stratum. •Uneven ground temperature caused by inclined-thermosyphon has aggravated disease in ITE during the past ten years.•A new embankment (HTE) was presented, and its cooling performance and heat transfer process were analyzed.•HTE performs much better than ITE in terms of temperature uniformity, cooling balance and efficiency.•Isoline width of −1.5 °C in HTE can be increased by 61%, and annual heat release can be enhanced by 72% compared with ITE.