Climate warming caused continuous degradation of permafrost on a global scale, especially in the Qinghai-Tibet Plateau (QTP), where the permafrost is dominated by warm permafrost. With the degradation of permafrost along the Qinghai-Tibet Railway (QTR), the stability of the embankment in permafrost regions is facing severe challenges.
There have been many researches on the cooling effect of active cooling measures adopted by QTR in permafrost regions, but few studies have been conducted on the ability of these measures as strengthening measures to cope with climate warming.
A team led by Prof. CHEN Ji from the Northwest Institute of Eco-Environment and Resources (NIEER) of the Chinese Academy of Sciences (CAS) discussed the cooling effects of crushed rock revetment (CRR) and thermosyphons, and studied the characteristics of permafrost degradation in this region during 2006-2018.
They selected the K1497+150 section of QTR, which is located in the southern lower limit of continuous permafrost on QTP, to analyze the thermal regime and deformation process based on ground temperature and deformation data.
Results showed that the permafrost in this area was degrading. Before the strengthening measures were applied, the permafrost under the embankment degraded faster than that under the natural site. The permafrost table under the natural site descended at a rate of 0.054 m per year from 2006 to 2009, much lower than that under the left shoulder, which was 0.09 m per year.
This study also found that the strengthening measures of CRR and thermosyphons could effectively improve the stability of the embankment in the warm and ice-rich permafrost region under climate warming.
The CRR slows the rising rate of the ground temperature by preventing heat transfer to the embankment in the summer. However, its cooling effect is weak for the deeper permafrost layer. CRR commonly used to strengthen QTR may not be effective in preventing degradation of underlying permafrost in warm and ice-rich regions under climate change.
The cooling ability of the thermosyphons in the winter contributes to increase the cold storage inside of the embankment, which could effectively resist the influences of climate warming. The coupling of the two measures makes the cooling capacity much stronger than that of a single one.
This study provides a reference for designing and strengthening of frozen soil embankment in warm permafrost regions in a warming climate.
The research results have been published in Advances in Climate Change Research entitled strengthening effect of crushed rock revetment and thermosyphons in a traditional embankment in permafrost regions under warming climate.
This study was supported by the Strategic Priority Research Program of CAS, the Natural Science Foundation of China, and the State Key Laboratory of Frozen Soils Engineering Foundation.
Variations in the ground temperature at different boreholes in 2006-2008. (Image by CHEN Ji)
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