Performance evaluation of a short-distance transition subgrade with pile-plank structures in high-speed railway

The transition subgrade is widely applied between the general subgrade and rigid structures (such as abutments, culverts, and tunnels) to reduce the degradation rate of track structures in high-speed railways. To address the problem that the common-type transition subgrade cannot be applied in mountainous areas due to the short distance between the tunnel and the subgrade (or abutment), a new type of pile-plank structure (PPS) transition subgrade for short-distance transition was proposed, and the PPS subgrade was successfully applied to a bridge-tunnel transition zone in the Shanghai-Kunming high-speed railway, China. A series of field tests, including vibration acceleration and velocity tests, were carried out in the bridge-tunnel transition zone to evaluate the transition performance of the PPS subgrade using the effective value and power spectral density method. In addition, an FE model that considers the coupled vehicle-track-subgrade-foundation interaction was established to fully reveal the dynamic performance of the PPS subgrade by characterizing the change rate of rail deflection, the dynamic response distribution of the track structure along the transition zone, and the running quality of the train comfort. The results show that the proposed PPS transition subgrade has a good transition performance and meets the requirements for excellent train comfort.