Study On The Temperature Control Method Of Permafrost Foundation Of Airport Runway In Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau is one of the world’s largest,highest,most glaciated and harshest plateaus due to climate and other reasons.Its unique climatic and geological conditions have brought great challenges to the construction of the airport runway.The difficulty of runway construction in permafrost area lies in the unstable properties of frozen soil and the fluctuation caused by temperature.Therefore,in this paper,with the help of numerical simulation software,under the background of global warming,combined with the characteristics of airport runway in this paper,the change law of runway foundation temperature field under different types of pavement,different width of pavement and different treatment measures of frozen soil in permafrost area was simulated and analyzed.The influence of different frozen soil treatment measures on the vertical displacement of runway foundation is also studied.The main work and achievements are as follows:(1)The influence of asphalt concrete pavement and cement concrete pavement on the temperature field of runway foundation is compared,and a conclusion is drawn.The results show that cement concrete pavement has better thermal stability and less disturbance to permafrost.By comparing and analyzing the temperature cloud map,the variation rule of ground temperature along depth and the melting depth of the runway foundation of the two types of pavement,it is found that the melting depth of the foundation temperature field of the cement concrete pavement is smaller,and the time in the melting state is one month shorter than that of the asphalt concrete pavement.In the design and construction of the runway,the choice of cement concrete pavement can reduce the disturbance of permafrost and improve the service life of the runway.(2)The temperature field of airfield runway foundation with cement concrete pavement with different pavement widths is studied,and the pavement with different widths is compared and analyzed by observing temperature cloud map,ground temperature variation rule along depth and melting depth data.The results show that the thermal stability of runway foundation becomes worse with the increase of runway width.This instability is manifested in the increase of ground temperature,the increase of melt core area and the deepening of melt depth.(3)After reviewing relevant literature,the filling replacement measures,heat insulation measures and combination measures are selected to treat frozen soil foundation,and the temperature field of runway foundation under different treatment measures is simulated respectively.Through the analysis,the following conclusions are drawn: The measure of sand and gravel filling has little influence on the temperature field of the runway foundation.In the early stage of runway operation in permafrost area,ground temperature of runway foundation in permafrost area increases slightly with the increase of filling depth,but the maximum melting depth of foundation decreases.In the later stage of runway operation,the filling with different depths has little influence on the maximum melting depth of runway foundation.The laying of heat insulation layer can effectively reduce the ground temperature of airport runway in permafrost area,reduce the maximum melting depth of runway foundation,and improve the thermal stability of permafrost foundation.Compared with EPS insulation material,XPS insulation material has better control effect on ground temperature of airport runway foundation in permafrost area.The thickness of the heat insulation layer also affects the temperature field of the foundation.Increasing the thickness of the heat insulation layer can reduce the temperature of the runway foundation and reduce the maximum melting depth of the foundation.In the combination measures,the heat insulation layer laid on top of the replacement soil has a better effect on reducing the ground temperature of the runway foundation and can reduce the maximum melting depth of the runway foundation more effectively than that laid on the bottom.(4)Based on the analysis of the maximum vertical displacement of runway foundation surface under different treatment measures of frozen soil,the following conclusions are drawn:Sand and gravel replacement measures have a great influence on the vertical displacement of airport runway surface in permafrost area.Increasing the filling depth can effectively reduce the maximum vertical displacement of the runway,thus improving the stability of the runway.The poor mechanical properties of heat insulation layer will increase the vertical displacement of runway surface.The increase of insulation layer thickness also leads to the increase of vertical displacement.The vertical displacement of runway made of XPS insulation layer is smaller than that of runway made of EPS insulation layer.In combination measures,the vertical displacement of runway surface in permafrost area is related to heat insulation material and laying position.EPS material is laid under the replacement soil,the vertical displacement of runway surface is small;However,the vertical displacement of the runway surface is relatively small when XPS material is laid above the replacement soil.