Study On Heat Insulation Effect Of High-rail Railway Base Covered In Seasonal Frozen Area

The northeast area of China is in the seasonal frozen soil region.The engineering construction of high-speed railway subgrade in this region will encounter overwintering problems due to objective factors such as the long duration and the inconvenience of the construction in winter.If insulation treat is not applied on the subgrade,the freeze injury will intrude into the subgrade and develop to natural soil layers with high water content as well as high frost heave property.Eventually,it will leave severe damage on the subgrade.Under the background of high-speed railway from Haerbin to Dalian,based on laboratory tests and computer simulations,this paper is aimed to explore the heat preservation of high speed railway subgrade covered by maize straws rather than insulation boards.Conclusions and results of this paper are displayed by the following:1)Experimental studies on temperature fields and water content fields of soils covered by maize straws with different thicknesses(0cm,10 cm,20cm and 30cm)are carried out,and the results of which prove that the soils covered with maize straws possess higher temperatures than those exposed to environment.The thicker the covering,the higher the temperature is.However,with the increase of the covering thickness,the increasing rate of heat prevention effect decreases gradually,and the relationship between these two variables is not simple linearity.Therefore,there is an optimal thickness when considering the economic cost and heat prevention effect.2)From the analysis on the water content fields of soils which are covered by maize straws with different thicknesses,it is revealed that the maize straw covering could efficiently prevent the evaporation of water from soil.Specifically,the thicker the covering,the slower the evaporation is,i.e.the conservation of soil moisture is better.3)By considering the boundary between the region of negative temperature and theregion of positive temperature,we could approximately obtain the relationship between the maximum frozen depth and the covering thickness,which indicate that when the covering thickness increases,the maximum frozen line moves up.For the cases of 20 cm and 30 cm coverings,there are no negative temperature regions in soils throughout the whole tests.Only for the case of 10 cm covering,the negative temperature region develops into soils.4)Computer simulation is used for analysis of the temperature fields under different covering conditions,say with covering or uncovered.The changing curves of temperature against time of soils at different depths are plotted from results of simulation,which are found to be in agreement with the laboratory tests.