Numerical Model for the Variation of the Frost Boundary below Embankments Using Surface Temperature and Net Radiation Data

Abstract

With the opening and running of the Qinghai-Tibet Railway (QTR) and the maintaining of the Qinghai-Tibet Highway (QTH) on the Qinghai-Tibet Plateau (QTP) in China, a lot of new ideas, methods and techniques were adopted and applied to the embankment engineering. Shading boards (awnings) are one of the permafrost protection measures that were used along the QTR and QTH. Because of the higher elevation and better atmospheric transparency, the QTP receives stronger solar radiation than other regions. This trend will be enhanced in the foreseeable future due to the worldwide climatic warming which affects the QTP more than other regions of the world. At the same time, the lower temperature permafrost changes into higher temperature frozen soil or even into thawed soil. In this paper we study the influence of awning (shading) measures at the slopes of a road or railway embankment on the radiation energy balance and ground temperature variation at and around a road or railway embankment. We report on new measurements of net radiation and ground temperature in a permafrost region and use these data as boundary conditions in a numerical finite element model. We find that awning measures along the embankment side slopes have a clear influence on the seasonal variation of the melting line and on the depth of the permafrost level. To some extent it can help to keep the permafrost under the road embankment cool and the permafrost level high, despite the degrading influence of the global climatic warming trend.