Dynamic Response of Pile-Net Composite Subgrade under Coupled Seismic-Train Load Effect

[Objective] With the rapid development of high-speed railways, the possibility of encountering earthquakes during train operation has significantly increased. Therefore, it is necessary to study the dynamic response of pile-net composite subgrades at different train running speeds and peak accelerations. [Method] Taking the CRTS Ⅱ plate-type ballastless track laid on the Beijing-Shanghai High Speed Railway as an example, a three-dimensional track-pile-net composite subgrade model is established using finite element software. Track vibration, dynamic stress transfer, pile forces, and driving safety are analyzed by applying train moving loads and seismic waves with subroutines. [Result & Conclusion] When the train runs at a higher speed, the resonance effect between the train and seismic is obvious, and the peak acceleration shows less effect on vertical track vibrations. The dynamic stress amplitude of foundation is dominated by seismic action, and the dynamic soil stress on the foundation surface shows a sudden increase. With the increase of horizontal distance, the pile-soil dynamic stress ratio exhibits a trend of first increasing and then decreasing, and the geogrid tensile stress gradually increases and turns negative when reaching the geogrid edge. The axial force and the bending moment amplitude of the pile body increase with the uplift of peak accelerations and train speeds. The closer the pile body is to the geogrid edge, the less it is affected by train operation speed. The train derailment coefficient in operation is less affected by the seismic peak acceleration, but is more affected by train operation speed. In case of earthquake, the operation safety can be enhanced by reducing train operation speed.