The Thermal Insulation Mechanism Of Ballastless Track Covered Ballast In Cold Area

China has a vast territory,a complex climate,and more than 1/2 of the territory is a cold area.Therefore,it is inevitable to build a ballastless track in cold area.Long-term operation practice has found that in the cold area,the cracks of the concrete surface,the peeling of the concrete surface,the exposed concrete,the powdering of the concrete,and the corrosion of the steel bars,etc.,have occurred in the cold areas.In order to ensure the stability and durability of ballastless tracks in cold area,it is necessary to adopt surface insulation measures for ballastless tracks in cold area.At present,most conventional insulation materials are various insulation foams,slag,and dry sand insulation.The foam insulation material is light in quality and low in strength,and easily falls off under high-frequency vibration of the train.Dry sand insulation is easy to absorb water,and the insulation performance is greatly reduced after water absorption.According to the complex operating environment of high-speed railways,this paper proposes insulation measures for covering the ballast layer on the surface of the ballastless track.This paper mainly studies the suitability of the ballast insulation layer.First,based on the basic principles of heat transfer,a ballastless track temperature field model is established to analyze the temperature characteristics of the ballastless track in cold regions.Through analysis,it is found that the temperature fluctuation of the ballastless track surface is large,the temperature difference between the inside and the outside is large,and the cooling rate is fast.Then,the temperature monitoring test of the ballast layer was conducted,and through the analysis of the test data,it was found that the heat conduction is mainly dominated in the ballast layer under the open interface and no wind condition;the ballast layer can effectively reduce the heat entry at high temperature and slow the heat loss at low temperature.Thermal insulation effect;the thermodynamic parameters of the ballast layer are calculated inversely according to the temperature amplitude attenuation formula.Finally,the thermal insulation effect of the ballastless track is analyzed in combination with the theoretical formula for calculating the surface insulation of the ballastless track.The calculation results show that the ballast layer can effectively reduce the temperature amplitude of the ballastless track surface caused by the periodic temperature change;during the cold wave,it can reduce the temperature drop amplitude of the ballastless track surface and slow down the cooling rate.