Theoretical models for the solar absorptivity of a roadway embankment

Abstract

Building roadways through permafrost corridors is challenged by the presence of permafrost stratum, which is sensitive to the changes of the heat transfer balance at the ground surface. Due to the construction of the embankment, some reflected radiation from the nearby ground is trapped and absorbed by the side slope. This additional absorption of the embankment may be detrimental to the thermal stability of the permafrost stratum but has not been understood. Here we present two theoretical models to estimate the solar absorption of the embankment and we compare the prediction by the models against the experimental measurements. One is the solar trapping model and the other is the surface roughness model. The former is relatively complicate but it can estimate the macro-reflectivity/absorptivity of the embankment and of the side slope, respectively. The latter is relatively straightforward but can estimate the macro-reflectivity/absorptivity of the embankment only. It is found that the embankment absorbs more sunlight than the adjacent ground and that for a typical embankment, the macro-absorptivity of the embankment is 0.01–0.05 lower than its micro-absorptivity. This minimal difference suggests that the solar absorption of an embankment can be curtailed by raising the embankment's albedo, which can be done by flatting the side slope surface and painting the slope with high-reflectivity.