Discrepancies of permafrost variations under thermal impacts from highway and railway on the Qinghai-Tibet Plateau

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Highway and railway lead to different variations of permafrost underlying their embankments owing to distinct thermal impacts from different embankment surfaces, which affects the designs and choices of engineering approaches to protect permafrost. However, the differences between these permafrost variations underlying highway and railway embankments are unclear. Employing a set of long-term soil temperature data on the Qinghai-Tibet Plateau, more than ten years of permafrost variations under thermal impacts from the Qinghai-Tibet Highway and the Qinghai-Tibet Railway have been analyzed and compared. The results show that the responses of permafrost under thermal impacts respectively from the highway and the railway were distinct with discrepancies in the long-term variations of the soil temperatures, the depth of permafrost table, their varying rates, and the characteristics of the sunny-shady effect. Such as, while the permafrost underlying a highway embankment kept warming and deepening its permafrost table, the permafrost underlying a railway embankment could slow the warming or maintain its thermal status or even become cooler. For instance, the permafrost table beneath the sunny slope shoulder of a highway site deepened from 5.94 m in 2003 to 8.98 m in 2020, with an increase of approximately 50%; however, on the contrary, the counterpart of a railway site shallowed from 3.40 m in 2006 to 2.13 m in 2020. Furtherly, the discrepancy of soil temperature deviation shows explicitly that, upon the underlying permafrost, a highway has more thermal impacts than a railway.