Thermal storage under an earthen roadway embankment over a permafrost region

Abstract

Building roadways in permafrost regions is always challenged because both roadway construction and global warming can induce the warming of the underlying soils. A group of permafrost cooling techniques has been employed to cool the embankment, with the focus on dropping the temperature of the underlying permafrost. To this end, understanding the thermal storage in the underlying soils after the embankment construction is critical to adopt the right techniques to drain the soils' heat at the right place. While the non-linear variation of heat absorption with depth in the permafrost under the embankment has been well documented, it remains unknown how to describe this situation mathematically. In this study, we innovatively propose a scalar ∆E to characterize the thermal storage of the soils under an earthen embankment over a permafrost region. It is found that immediately after the embankment was built, the soils at 0–3 m depth are cooled down while those at 3–6 m depth are warmed up. However, the temperature variations of these soils, in shape and in trend, are different from the thermal storage of the soils. The profile of temperature variation versus depth changes continuously, while the profile of thermal storage versus depth varies abruptly at the interfaces of soil layers. The reason is that most heat entering the permafrost stratum is stored in water-rich soils while a limited heat is deposited in water-poor soils. This finding suggests that permafrost cooling techniques shall be considered to drain the thermal storage in the water-rich soils primarily.