Numerical Study on Cooling Effect of Closed Crushed-Rock Embankment along Qinghai-Tibet Railway in China

Abstract

At present, crushed-rock embankment has been widely utilized as a method for avoiding thaw settlement of roadbed in the construction of Qinghai-Tibet Railway of China. The ballast layer and crushed-rock layer can be regarded as porous media in railway embankment. It is windy on the Qinghai-Tibet Plateau, so that the crushed-rock embankment is often covered by sand or snow on its surfaces and a special closed space is formed in its crushed-rock layer. In this paper, in order to research the cooling effect of crushed-rock embankment on the underlying permafrost under the closed condition, based on the special climatic and geological conditions of Qinghai-Tibet Plateau, a numerical representation of the unsteady two-dimensional continuity, momentum and energy equations of thermal convection for incompressible fluid in porous media is used to analyze the temperature characteristics of closed crushed-rock embankment for 50 years. The results indicate that, under the assumption that the air temperature will warm by 2.6 °C in the future 50 years in the areas where the present mean annual air temperature is −4.0 °C, when the crushed-rock embankment is covered by sand or snow, it can still protect actively the underlying permafrost; However, with the augment of embankment height (embankment fill thickness on crushed-rock layer), its cooling effect becomes weak.