To investigate the ground vibration of unsaturated ground subjected to moving loads caused by high-speed train

a two-and-a-half-dimensional finite element method (2.5D FEM) was deduced. The foundation was considered as three-phase medium

and the Euler beam model was used to simulate the track system. The 2.5D FEM equations were derived by using the Galerkin method and the Fourier transform with respect to time and load moving direction. The solution in the frequency-wave number domain was transformed to the time-space domain through the Fast Fourier Transform (FFT). The influences of train speed and water saturation on ground vibration and excess pore water pressure were analyzed. Results show that at the track center

ground vibration displacement amplitude increased significantly as the soil varied from near saturated (Sr=99%) to fully saturated state.At a given speed

the unsaturated ground acceleration amplitude was larger than that of the saturated ground

and it decreased more rapidly over time than the saturated ground. At 8 m away from the track center

the unsaturated ground acceleration amplitude was far greater than that of the saturated ground at the same speed. but

when the train speed was beyond 300 km/h

their displacement amplitudes tended to be equal. The ground vibration amplitude attenuated rapidly near the track center

while it attenuated slowly beyond 5 m. The excess pore water pressure of the unsaturated ground under the track center was mainly distributed in shallow depth (0~4.5 m beneath the ground surface) and the peak value appeared at about 1.8 m

which decreased sharply as the ground saturation decreases.