Strengthening effect of crushed rock revetment and thermosyphons in a traditional embankment in permafrost regions under warming climate

The embankment of the Qinghai-Tibet Railway(QTR)has been experiencing severe problems due to permafrost degradation,especially in warm and ice-rich permafrost regions.Based on ground temperature and deformation data of the embankment at location K1497+150 of the QTR in 2006-2018,the thermal regime and deformation process were analysed.The results showed that 1)the degradation rate of permafrost under the embankment was faster than that under the natural site without engineering construction,and 2)the deformation rate of the embankment had exceeded the safety range for the QTR embankment before adopting mitigative measures.In addition,this study evaluated the cooling effect on the underlying permafrost and working mechanism of two strengthening measures.Two measures,crushed rock revetment(CRR)and thermosyphons,were adopted to protect the underlying permafrost from continual degradation.The individual cooling effect of the CRR was not as good as that of the thermosyphons.However,the combination of the two could enhance the protective effects of each on the underlying permafrost,effectively cooling the permafrost and improving the stability of the embankment.

Numerical optimization on differential adjusting measures for asymmetrical degenerated warm permafrost railway embankment

Affected by climate warming and shady–sunny slope effect,the permafrost foundation under the railway is undergoing a significant asymmetric degradation process;research on the corresponding regulating or strengthening measures is urgently needed.Based on a well developed of numerical model,we analyzed the‘thermal repair’effect of three redesigned differential thermal reinforcement on the partially degraded permafrost embankment with steps.The results show that,when used as a strengthening measure,the method of laying crushed rock revetment(CRR)with different thicknesses on the sunny and shady slopes cannot completely eliminate the residual warm permafrost regions formed in the previous thermal erosion.When the TCRR scheme is adopted for reinforcement,although horizontal region from the evaporation section of thermosyphones(TPCTs)to the right side of the embankment is remarkably cooled,permafrost under the sunny slope is still deteriorating.In the long run,both ETCRR and TCECRR reinforcement schemes can produce a large range of‘cold core’right below the whole embankment.However,from the perspective of the simultaneous functioning range and cold storage capacity,the TCECRR scheme is signally more efficient.The thermal insulation materials in the above composite strengthening measures can not only resist the heat input in the warm season,but also improve their working efficiency by maintaining the temperature difference between the evaporation section of the heat pipe and the external environment in cold season.The addition of crushed rock revetment in TCECRR has played its thermal semiconductor effect and further improved the comprehensive thermal repair efficiency of the composite measures.