Albedo increment as a scalar of the sunny-shady slope effect of roadway embankments in permafrost region

Abstract

Roadways in permafrost region are usually built on embankments that are placed on the natural ground to reduce construction-induced thermal disturbance. The embankment alters the thermal regime of the soil under natural ground such that the soil under the south-facing side slope is warmer than that under the north-facing one. While this sunny-shady slope effect (SSE) has been well documented, how to mathematically describe this effect remains unknown. This study derives a simple straightforward scalar ΔR to characterize the SSE of an embankment in permafrost region. The scalar ΔR correlates to the internal factors such as the side-slope albedo, the side slope angle, and the embankment orientation etc., and to the external factors such as the instantaneous and seasonal solar irradiance and the sky cleanness factor. Increasing albedo of the south-facing side slope in a value of ΔR eliminates the SSE. The scalar ΔR was verified by simulating an east–west embankment with a side-slope angle of π/4 and an initial side-slope albedo of 0.25. The simulation revealed that the SSE is apparent in case of business-as-usual scenario but is eliminated in case if albedo of the south-facing side slope increases ΔR = 0.21. It is expected to study if ΔR correlates to the embankment differential settlement, the underlying permafrost temperature and the pavement longitudinal cracks.