An experimental study of reflective shading devices for cooling roadbeds in permafrost regions

摘要

The irradiance values on the Qing-Tibet Plateau are higher than those on other regions with the same latitude, a factor that is challenging the roadways built on degrading permafrost. An alternative to preserve the permafrost stratum is to install shading devices, such as shading boards, on the side slope of roadway embankment for reducing the solar absorption of embankments. The shading boards, however, are not popularly used because they are prone to wind damages. Here we offer a new reflective shading device that reduces the risk of wind damages and cuts the heat gain of the soil simultaneously. By making the top-side of shading devices highly reflective, the heat gain of the device is greatly reduced so that the air gap between the board's bottom and the soil is greatly diminished. A field experiment is conducted to observe the temperatures of the device and of topsoil under the device and to measure the heat flux at the bottom of the device. Temperature observations verify that the shading device with a high albedo at the topside can keep the topsoil cool. Heat-flux measurements substantiate the high-albedo shading devices cut down the heat gain of the soils. Increasing the albedo of shading devices can promote the use of such devices as a permafrost-cooling strategy.