Research On Dynamic Response Characteristics And Long-term Dynamic Stability Of Transition Zone In High-speed Railway

In recent years,high-speed railways have developed rapidly around the world.With the gradual increase in train speeds,the requirements for subgrade structures have become higher and higher.As the weak link of the high-speed railway ballastless track subgrade,the research on dynamic response characteristics and long-term dynamic stability of transition section subgrade is of great significance.Based on the National Natural Science Foundation of China,this paper analyzes the dynamic response characteristics of the transition zone before and after commercial operation based on the field dynamic response test results of two transition zones of the Wuhan-Guangzhou high-speed railway,and the long-term dynamic stability of the transition zone subgrade was comprehensively evaluated and the dynamic response of the subgrade-bridge transition zone was simulated and calculated.The main work and conclusions of this paper are as follows:?1?Based on the field dynamic response test results of the subgrade-bridge transition zone in the“comprehensive commissioning test”period and 2 years after the commercial operation,the dynamic response characteristics of the transition zone before and after commercial operation are analyzed.The results show that:?1?The vibration acceleration of the subgrade surface and the vibration velocity and dynamic displacement of the asphalt concrete layer increase with the increase of the distance from the abutment tail.?2?The increase in subgrade stiffness or the increase in train speed will increase the peak frequency of subgrade vibration and transfer the vibration energy to the high-frequency part,and the superior frequency of subgrade vibration is mainly determined by the train speed and the geometric size of the train.?3?After 2years of commercial operation,the peak frequency of the same measuring point of the transition zone subgrade remains unchanged,the total vibration energy and the vibration energy of each frequency band have been reduced overall,and the overall smoothness of the subgrade-bridge transition zone has improved.?2?Based on the calculation results of dynamic shear strain of the transition zone subgrade,the linear correlation analysis between the vibration speed and the train speed,and the comparison of the vibration speed before and after commercial operation,the long-term dynamic stability of the two transition zone subgrades was comprehensively evaluated.The results show that:?1?The subgrade vibration increment caused by passage of train on the adjacent line cannot be ignored in the calculation of dynamic shear strain of the transition zone.?2?The ratio of the maximum value of dynamic shear strain at each measuring point of the transition zone subgrade to the average volume shear strain threshold?_tv,M is less than 20%,which meets the requirements of dynamic stability.?3?The vibration speed of the transition zone subgrade has a good linear correlation with the train speed.?4?After 2 years of commercial operation,the vibration velocity amplitude of the transition zone subgrade has been reduced overall,and the longitudinal distribution law along the line remains unchanged.Based on the above results,it can be determined that the transition zone subgrade has good long-term dynamic stability.?3?A three-dimensional dynamic coupling model of train-track-transition zone is established,and the dynamic response of subgrade-bridge transition zone is simulated and calculated.The results show that:?1?The most unfavorable distribution range of the dynamic response of each structural layer along the line appears in the bottom unreinforced area 15.6?28.6m away from the abutment tail,and the dynamic stress amplitude of the subgrade in the trapezoidal reinforced area decays linearly within a certain depth range.The absorption effect of graded gravel+5%cement on the vertical vibration of the subgrade is better than that of the A group filler.?2?Compared with the normal trapezoid and inverted trapezoid transition forms,the combined transition form as the transition zone setting method can better realize the smooth transition between the bridge and the subgrade.