Study On Runway Subgrade Application Of L Heat Pipe-insulation Plate In Permafrost Regions

According to the development plan of civil aviation,China will build multiple airports in the permafrost zone.At present,the research on the temperature control technology of the airport runway roadbed in the permafrost zone is still blank.In order to solve the thermal stability problem of runway pavement foundation,based on the idea of active cooling and thermal insulation,research on the temperature control technology of frozen soil of L-type heat pipe-insulation board composite pavement foundation was carried out.The main work and results are as follows:1.According to the cooling mechanism of the heat pipe and the heat preservation board,the soil temperature control equation is established.Based on the characteristics of the heat pipe,the heat resistance relation of the heat pipe is proposed,and the heat transfer model between air,heat pipe and soil is is established.2.The indoor test of L-type heat pipe and insulation board was carried out.Firstly,the cooling effect of three kinds of heat pipes made of industrial pure aluminum,Q235 carbon steel and 304 stainless steel is compared,which indicates that the cooling effect of industrial pure aluminum heat pipe is the best.Then the influence of pure aluminum heat pipe on horizontal Angle,bending Angle,effective cooling radius and cooling range of evaporation section were tested.Based on the parameters of heat pipe with the best cooling effect in cold season,the thickness and buried depth of insulation board were tested.The results show that:(1)In the range of the larger the horizontal Angle from 10° to 45°,the more obvious the cooling effect,but the difference in the range of cooling amplitude with different bending angles is small,and the temperature difference ranges from 0.1?to 0.3? at the same depth.(2)The effective cooling radius of the heat pipe is from1.6m to 1.8m.(3)The cooling range of the heat pipe is between 1.7? and 5.6?.(4)The return temperature curve of the soil layer of the insulation plate with the thickness of 3cm and 5cm is every close to each other,and the temperature is relatively low near the heat pipe,so it is appropriate to select the insulation plate with the thickness of 3cm.(5)The subgrade insulation effect is better under the buried depth of 30 cm because the return rate is relatively slow.It can be buried in the cushion layer of 30 cm,between the cushion layer and the insulation board with gravel bedding.Experimental results show that L-type non-standard heat pipe and insulation board can reduce the soil base temperature and provide a basis for the relevant structural design parameters3.A numerical model was established to verify the cooling effect of indoor test was verified,and compare the law of temperature variation including natural subgrade and pavement subgrade,L type heat pipe-insulation board composite channel base.The results show that under the same conditions,the temperature of runway subgrade is higher than that of natural subgrade,and the temperature increase is larger than that of natural subgrade.And the thermal stability of permafrost base is lower.The runway subgrade is more degraded 2m~2.5m than the natural subgrade.The upper limit of frozen soil degradation is as much as 2m~2.5m,the maximum temperature rises about 3?.The L heat pipe-insulation plate composite channel can reduce the temperature of subgrade,decrease the maximum temperature peak,decrease the depth range of thawing area,increase the upper limit of permafrost 1.5m.The effective cooling radius of a single heat pipe is about 2m,and the degradation trend of frozen soil is slowed down.