Application of the roadbed cooling approach in Qinghai–Tibet railway engineering

The Qinghai–Tibet Railway goes through 550 km of permafrost, half of which is classified as “warm” permafrost with a mean annual ground temperature ranging from 0 to − 1 °C. The Qinghai–Tibet Railway is a long-term plan. In order to maintain its normal operation, climatic changes over the next 50 to 100 years need to be considered. The passive method of simply increasing the thermal resistance by raising embankment height and using insulating materials has proven ineffective on “warm” permafrost and therefore cannot be used in the construction of Qinghai–Tibet Railway in “warm” and ice-rich permafrost area. To deal with the “warm” nature of the plateau permafrost and global warming, a series of proactive roadbed-cooling methods were employed, which include solar radiation control using shading boards, heat convection control using air ducts, thermosyphons, and air-cooled embankments, and finally heat conduction control using “thermal semi-conductor” materials. A proper combination of these measures can enhance the cooling effect. All these methods can be used to lower the ground temperature and to help stabilize the Qinghai–Tibet Railway. Especially, the air-cooled embankments have the advantages of high efficiency, ease of installation, environmental friendliness, and relative low cost.