Abstract: The sunny and shady slope effect exerts significant impact on the construction quality and operation and maintenance of road engineering in cold regions. Coating the embankment surface with materials of light color or high reflectivity will improve the anti-radiation ability of subgrade slope, intensify the cooling effect of crushed rock layer, and remarkably reduce the received net radiation. An energy absorption model for crushed rock rough surface is established to deduce the relationship between the macro-reflectivity R and the micro-reflectivity r on the surface of rough crushed rock. In association with image processing, the reflectivity of crushed rock layer is estimated by obtaining the area of crushed rock and cavities. Furthermore, the reliability of the established model is verified by measured data. Analysis on model parameters reveals that reducing the roughness of rock surface and the ground clearance degree are conducive to improving the reflectivity of the whole crushed rock layer. Roughness of crushed rock severely inhibits the improvement of macro-reflectivity R. In addition, the selection of coating material should be depended on the roughness, and we recommend the reflectivity of coating between 0.4-0.6.

Key words: crushed rock layer, sunny and shady slope effect, multiple reflectance, reflectivity, roughness, image processing, permafrost