Multi-scale Study On Dynamic Response And Contact Degradation Of High-speed Railway Subgrade Surface

China is in an important historical period of rapid development of high-speed railway Since the opening of the first Beijing-Tianjin inter-city high-speed railway in 2008,the total mileage of high-speed railway in China has exceeded 29,000 kilometers.Because the ballastless track has the outstanding advantages of good rigidity uniformity,high track stability,strong structural durability and less maintenance work,it is widely used in China's new high-speed railway lines.The operation practice found that under the influence of the long-term effects of engineering cyclic load and rainfall seepage,the contact position between the concrete base plate of the ballastless track and the surface layer of the subgrade caused some diseases,typical diseases such as contact under the base plate are voided,and the base plate is smeared and muddy.These diseases increases the workload of maintenance and repair.If not treated in time,other types of diseases will be induced,and in severe cases,driving safety will also be affected.Therefore,research on the contact mechanism between the surface of the subgrade and the base plate of the ballastless track has important theoretical significance for ensuring long-term stability and safe operation of the high-speed railway.The paper studies the dynamic response of the surface gravel of the subgrade and the contact problem between the graded gravel and the track structure.The simulation models are established by the finite element method and the discrete element method.The dynamic response and contact characteristics of the gravel were analyzed macroscopically and meticulously.The main contents of this paper are as follows:1.Establish the finite element model of vehicle-track-subgrade,and the dynamic response of subgrade surface under high-speed train load is calculated and analyzed.The calculation results are compared with the field measured data to verify the correctness of the model.The distribution and propagation law of additional dynamic stress of subgrade are obtained by calculation,and the energy absorption mechanism of subgrade soil is analyzed.2.Based on the results of finite element model,the non-contact area between the concrete base plate and the surface of subgrade is set up by referring to the maximum additional dynamic stress position of the subgrade,and the deterioration and expansion law of the non-contact area is analyzed.The results show that when the contact deterioration area of subgrade surface expands in rectangular shape,its aspect ratio is between 2 and 3.3.The DEM-FDM coupling model of track structure-subgrade surface is established,and the train load calculated by finite element method is fitted into a harmonic impulse load and added to the DEM-FDM coupling model to calculate and analyze the dynamic response of graded gravel,such as force,displacement,velocity and acceleration.The validity of the model is verified by the measured data of relevant literatures.4.Based on the results of the DEM-FDM coupling model,the cracks in the asphalt concrete protective layer are set on the edge of the concrete base plate,and the effects of different crack widths on the dynamic response of graded gravel are calculated and analyzed.