Performance Analysis Of CRTS Ⅲ Track Structure With Thin Layer Of Asphalt Concrete In Northeast Seasonal Freezing Area

At present,the length of high-speed railway in operation in China has exceeded 40,000 km,making it the longest in the world.With the rapid development of high-speed railway,China has independently developed CRTS III ballastless track with complete intellectual property rights based on the advantages and disadvantages of CRTS I and II ballastless track in service of the previous generation,and gradually promoted it throughout the country.Traditional ballastless track structure subgrade sealing layer is mainly cement concrete,with the long-term service of the structure,cement concrete material damage is serious,it is difficult to meet the long-term waterproof performance of the structure.Asphalt concrete material has high water resistance,and its viscoelastic properties can play a role in damping and noise reduction of the structure.In the land area of China,the seasonal freezing climate region accounts for more than half.In order to promote the asphalt concrete water-sealing layer combined with the CRTS III plate-type ballastless track with independent intellectual property rights in China to serve in the seasonal freezing region,it is necessary to explore the temperature field characteristics of the structure under typical climatic conditions in the seasonal freezing region.The evolution law of stress and strain and damage trend of track structure under adverse daily temperature load and cyclic temperature load are analyzed,and the position of adverse load and dynamic response of structure layer under train load are studied.On this basis,the corresponding engineering measures are put forward to improve the stress state of the structure,which has important engineering significance to improve the service performance of the structure.The main research contents and conclusions of this paper are as follows:According to the basic theory of heat conduction,the analysis model of spatial static thermal effect of ballastless track with thin layer of asphalt concrete sealing layer and its subgrade is established.Based on the typical meteorological data of Harbin in recent years in seasonal freezing area,the distribution characteristics of temperature field of ballastless track structure with thin layer of asphalt concrete layer are studied.Based on the calculated results of temperature field under adverse climatic conditions(high solar radiation days in summer and low temperature days in winter),sequential coupled thermal analysis was carried out.The mechanical and deformation characteristics of track structure under the action of temperature gradient and temperature load cycle are studied,and the interlayer interaction relationship between asphalt concrete layer and adjacent structural layer and the damage trend of track structure are explored.The dynamic analysis model of train-asphalt concrete ballastless tracksubgrade is constructed,and the mechanical response of asphalt concrete layer under train load is simulated.Research shows that:(1)The daily temperature of the orbital structure shows a sinusoidal periodic variation with a certain lag compared with the daily temperature variation.The diurnal temperature variation curve of track-subgrade structure at different depths presents an inverted cone,and the diurnal temperature variation is more severe in the depth range of 0-0.3m.The diurnal temperature variation of track structure greater than 0.3m is within 5℃,and the temperature tends to be the same within a day when it reaches a certain depth of subgrade.The temperature of the track structure is symmetrically distributed along the transverse direction.The temperature changes greatly in the range of 0.25 m away from both sides,and the temperature drops suddenly at 0.5m away from both sides.(2)The daily temperature variation amplitude of the unexposed asphalt concrete layer at the bottom of the track structure is less than 1℃,and the temperature gradient is less than13℃/m,which is little affected by the external environmental temperature.The asphalt concrete layer between the road shoulder and the line is directly exposed to the atmosphere.The maximum negative temperature gradient is 62.5℃/m in the lowest temperature condition,and the maximum positive temperature gradient is 126.6℃/m in the highest temperature condition.After the addition of asphalt concrete layer,the temperature of subgrade under the layer is reduced by 1.5-2.5℃ year-on-year,which has a good heat insulation effect.(3)The total solar radiation is the most significant factor affecting the temperature change of the orbital structure.Considering the maximum positive temperature gradient under each working condition comprehensively,the wind free weather with strong solar radiation was taken as the most unfavorable climate condition in the northeast seasonal frozen region,and the maximum positive and negative temperature gradient of the structure was 283.5℃/m and-24.9℃/m,respectively.(4)Under the action of temperature load(and low temperature load)of sunny day and high radiation all day,the longitudinal stress of the track plate at the top of ballastless track structure and the asphalt concrete layer at the bottom is about 3 times of the transverse stress,and the maximum stress occurs at the expansion joints and four corners of the structure layer.The displacement of each layer of track structure is symmetrically distributed and decreases layer by layer.In sunny days with high radiation,the maximum longitudinal displacement of the base plate at the expansion joints at both ends reaches 1.7mm.Under single-day temperature load,the structure is prone to damage in the four corners of the expansion joint on the side of the contact panel.The damage development trend at the corner of the plate in summer is greater than that in winter,and the damage development trend at the expansion joint in winter is greater than that in summer.(5)Under the action of cyclic temperature,the structural stress and strain change periodically with temperature.The maximum tensile stress of asphalt concrete layer at expansion joint is stable at 0.44 mpa in winter under low temperature cycle,and the maximum compressive stress at the same position is stable at 0.1mpa in summer.The asphalt concrete layer and the base plate are bonded.In the actual construction process,the interaction between layers can be reduced by choosing the appropriate construction temperature or laying the composite geometric sliding layer structure,and the cracking of asphalt concrete waterproof sealing layer can be improved.(6)The expansion joint of base plate is the most unfavorable position of wheel set,and transverse crack is more easily caused by train load.After the addition of asphalt concrete layer,the vertical acceleration and displacement of each structural layer decrease,which can alleviate the vibration and settlement of the structure,and its effect is most obvious in the base plate layer.The effect of temperature load in the coupling load is greater than that of train load.