The subgrade frost boiling under ballastless track is a special form of high-speed railway subgrade defects appearing in recent years. In order to study the effect of the frost boiling on dynamic characteristics of ballastless track subgrade

in-situ survey and train-induced vibration tests were carried out in Shanghai-Nanjing intercity railway defects section. The vibration characteristics of ballastless track subgrade under the condition of forst boiling are analyzed. The results show that the subgrade frost boiling mainly resulted from the high content of fine particles in graded gravel and the cracking in expansion joints and side joints of foundation plate. The frost boiling at subgrade bed reduces the support and constraint effect of subgrade on the ballastless track

and intensifies the vibration of ballasted track structure

especially to the foundation plate of ballastless track. The vibration amplification effect increases with the increase of train speed. The defect also changes vibration wave transmission between ballastless track and subgrade bed

which restricts the energy dissipation function of subgrade bed. When the train speed reaches 247 km/h

the amplitude of vibration displacement at the surface of subgrade reduces by 45%. The vibration displacement transfer function from the foundation plate to subgrade bed decreases by 2/3

and the value is between 0.22-0.39 in dynamic loading mainly frequency range (0~15Hz) of the subgrade.