Recent research on the track-subgrade of high-speed railways

The safety and comfort of high-speed trains raises the strict demands on the performance of the track subgrade system during the service life over 100 years, for example, strict post-construction settlement at millimeter level, appropriate dynamic stiffness, and long-term durability. Under extreme climatic conditions such as heavy rainfall, persistent drought, and extreme low or high temperatures, long-term dynamic loading on the track-subgrade will cause many engineering problems, including excessive settlement. When the train speed equals the critical speed, the resonance of the track-subgrade causes a great increase in the vibration level. In practice, due to the high quality of fill material used in the subgrade construction, the critical speed is always higher than the train speed. Hence, the resonance can hardly be observed through field monitoring and model tests.