Study On The Thermal Effect And Treatment Measures Of Sunny-Shady Slope On The Permafrost Embankment Along The Qinghai-Tibet Highway

The Qinghai-Tibet engineering corridor is in the direction of northeast-southwest,and there are strong solar radiation and high air transparency of the Qinghai-Tibet Plateau.The sunny-shady slope effect widely exists in the engineering embankment in the corridor.Due to the sunny-shady slope effect,embankment settlement on sunny side is generally greater than the shady side,which triggered a series of engineering damages,including roadbed inclination,slope slip and longitudinal cracks.These damages not only seriously undermined the stability of the embankments,but also greatly increase the operation and maintenance c ost in the later period of the project,which poses a great threat to the safe operation of the planned and built engineering buildings.Therefore,in order to provide scientific basis for the prevention and control of the highway embankment engineering diseases in permafrost region,it is very important to study the mechanism of the heat effect of the sunny-shady slope.In the study of the sunny-shady slope effect in the embankment,less focus on the difference of the thermal state between sunny-shady slope,and great focus on the long-term thermal state of the symmetrical embankment in the past.Even in the study of the sunny-shady effect,the difference of artificial permafrost table beneath the left and right shoulder was only concerned,but the differential freezing-thawing process of the embankment is not taken into account,which is closely related to the problems of the embankment and pavement damages.Therefore,aiming at the thermal effect sunny-shady slope effect in the corridor.Considering the field measured date of the typical sections along the Qinghai-Tibet Highway(QTH),I will systematically discussed the freezing-thawing characteristic of the shallow soil on the sunny-shady slope,the seasonal freezing-thawing process,the artificial permafrost table beneath the embankment and the difference development process of thawed bulb on the following: the embankment orientation,embankment height and the mean an nual air temperature(MAAT).And simulation study on horizontal heat affected under two parallel road status are carried out.Meanwhile,thermosyphons are widely used to maintain the stability of the embankment along Qinghai-Tibet engineering corridor.And the treatment effect of the embankment sunny-shady slope under different layout schemes is studied on the basis of the layout of thermosyphons,which it is expected to give out theoretical reference for future construction and maintenance of roadway engineering in the Qinghai-Tibet engineering corridor.Based on the above research,the following conclusions are obtained:(1)Under the background of climate warming,the freezing(melting)index of the left and right shoulder along the QTH embankment has been declining,while the melting index of the left and right shoulder has been raising year by year.The difference of freezing index of the shallow soil on the sunny-shady slope is more obvious than that of thawing index,especially the most obvious difference between the EW orientation,which is about 2.36 times of that on the sunny slope for the embankment,which is little difference between the thawing index of the shady slope.(2)The sunny slope for the embankment is always ahead of the thawing(freezing)period,and later enter the freezing period of the shady slope.The maximum difference in the freezing and thawing period of the two slopes can be as much as one month for the embankment in EW orientation.And there is little difference in NS orientation.The asymmetrical distribution of freeze-melt state of under the high embankment is more obvious than that of ordinary embankment in the same period.Therefore,it is easier to cause transversal differen tial settlement of the embankment and damage of the longitudinal cracks.(3)After the embankment construction,the artificial permafrost table beneath shady slope has a certain uplift,and the longest uplift time is about 22 years in EW orientation.Then,the artificial permafrost table declines quickly beneath the sunny and shady slopes,and the maximum decline rate can be as much as 20 cm/a.(4)The cooling effect of thermosyphon embankment has a positive effect on relieving the sunny-shady slope effect,which have a certain uplift of the artificial permafrost table on the side of thermosyphons and keep it 3.3m.the maximum decrease of ground is about 4°C in the depth of 4-8m below the embankment surface.Since the climate warming,the temperature of the ordinary embankment and the thermosyphon embankment increase slowly.In the depth of 8m below the embankment surface,the decrease of the thermosyphon embankment is only 0.2~0.6°C.(5)Overall,in regions with mean annual ground temperature(MAGT)lower than-1°C,because the thermal stability of permafrost beneath embankment is better,which can be used one-side type thermosyphon.In regions with MAGT higher than-1°C,because the thermal stability of permafrost beneath embankment is poor,which can be used two-side type thermosyphon.When the thawed interlayer is beneath embankment,it can be use the inclined type thermosyphon.(6)The separate embankment not only bring more heat to the soil,but also affects the temperature distribution of the embankment soil when the distance more closer.To ensure thermal interference can be ignored of Qinghai-Tibet Expressway,the transverse direction distance constructed with monolithic architecture model is about 10 m.