Radiation Effect of Shading Board on Embankment Side Slope on Tibetan Plateau

Because of the higher elevation and better atmosphere transparency,the Tibetan Plateau has stronger radiation than other regions,which let the daily variation of ground surface temperature more obvious.The shading board measure is one of the active protecting permafrost measures,which has been adopted widely along the Qinghai-Tibet railway and highway.The main contribution of the shading board measure is to cut off the sun radiation directly come to ground surface,and to reduce the net radiation and heat flow entering into the embankment,which ensure the embankment temperature lower,the roadbed permafrost stationary and embankment safety.The field test shows that the mean net radiation into the embankment is 300~350 W·m-2,but it is 30~45 W·m-2 under the shading board,80%~90% decreasing of the nature net radiation.The shading board make the heat flow entering into embankment reduce 50%~75%.At the same time,the shaded ground surface temperature is 6~8 ℃ lower than original embankment.All the test results show that the shading board measure can reduce the net radiation and heat flow into the embankment rapidly and effectively,then,it is possibly to lower the embankment height and the temperature inside the embankment,to delay the soil temperature rising effectively under the globe warm background,to ensure the embankment stable and safety,and to guarantee the roads unblocked in cold and permafrost regions.