Over one half of the permafrost along the Qinghai-Tibet Railway is "warm" and approximately 40% ice-rich. Under global warming, the construction of the Qinghai-Tibet Railway needs to consider climate changes over the next 50-100 years. Recent estimates indicate that the air temperature on the plateau will increase by 2.2-2.6 degrees C by 2050. Thus, the key to the success of the railway construction lies in preventing the permafrost underlying roadbeds from thawing. It has been more than 100 years since the first railway was built over permafrost. A frost damage ratio of greater than 30% has been reported for all the railroads built in permafrost regions. Based upon the experience and lessons learned from roadway constructions over permafrost, this paper proposes a more proactive design approach for the construction of the Qinghai-Tibet Railway. This approach focuses on cooling down the roadbed by lowering the ground temperature and is different from the passive method of preventing permafrost from thawing by simply increasing thermal resistance (e.g., increasing embankment height and using insulating materials). This "roadbed cooling" design approach is especially relevant to "warm" and ice-rich permafrost areas. A number of measures can be taken to cool down the roadbed, including proper selection of roadbed material and configurations to adjust solar radiation, heat convection, and heat conduction patterns in and/or around the roadbed. (c) 2005 Elsevier B.V. All rights reserved.
