Research On Performance And Cracking Mechanism Of Asphalt Concrete Layer Under The Ballastless Track Of High Speed Railway

High-speed railway has the advantages of high safety,high speed and high smoothness.It has developed rapidly in China in recent years.As the basis of the track structure,the strength,rigidity and stability of roadbed are of great significance for the safe operation of trains.The condition of subgrade is closely related to the water content.Therefore,various anti-drainage measures need to be taken in the actual project to prevent the roadbed from water.As asphalt concrete has the characteristics of viscoelasticity,strength and flexibility,it is gradually replacing cement concrete in the waterproof layer of subgrade of high-speed railway.However,it is found that the asphalt concrete layer under the ballastless track has cracking disease in the operation,which has reduced the waterproof function and caused diseases such as mud-pumping,posing a great threat to the high-speed railway.Therefore,the cracking problem of the asphalt concrete layer under the ballastless track of high-speed railway needs to be solved urgently.In this paper,the asphalt concrete layer under the track structure is taken as the research object,and the generalized Maxwell model is introduced as the viscoelastic constitutive model.First,the static and dynamic model of track structure,asphalt concrete layer and subgrade are established.Then the mechanical properties of asphalt concrete layer under temperature load and train load are studied and the causes of cracking are analyzed.Besides,the cracking process of asphalt concrete layer is analyzed by extended finite element model.Finally some relevant suggestions are provided for improving the stress state of asphalt concrete layer and promoting the application of the asphalt concrete layer.The research shows that under the temperature load,asphalt concrete layer near the expansion joints of the base plate has large deformation.Consequently,fatigue damage will occur in these positions of asphalt concrete layer under the long-term temperature load,which is consistent with the actual project.Under the train load,the expansion joints of the base plate change the distribution of stress and strain of asphalt concrete layer.These positions are also unfavorable,but there is no risk of one-time cracking.The cracking of asphalt concrete layer at low temperature is mainly caused by temperature load not train load.But the edges of base plate have obvious lateral shearing effect on asphalt concrete layer at high temperature because of the train load.The cracking of asphalt concrete layer in the position of expansion joints of the base plate starts from the middle,and the vertical crack is formed and then spreads laterally to both sides.When it comes to engineering proposals,it is proposed to lay a composite geomembrane sliding layer on the sides of the expansion joints of the base plate at 1.0-1.5 m,or to strengthen the interaction between the asphalt concrete layer and the surface of the subgrade,which can extend the service life of the asphalt concrete layer.In addition,combined with the deformation and fatigue life of the asphalt concrete layer under the train load and temperature load,it is recommended that the thickness of the asphalt concrete layer should be at least 8.0 cm.Considering the dynamic deformation of the surface layer of subgrade,the modulus of the asphalt concrete layer should be at least 7000 MPa.