Ground Vibration Induced by Moving Train Loads on Unsaturated Ground Using 2.5D FEM

Vibration of an unsaturated ground subjected to moving train loads is investigated using a two-and-a-half-dimensional finite element method (2.5D FEM). The track system is simplified as an Euler beam resting on the unsaturated porous medium, the governing equations are transformed to the frequency–wavenumber domain, and the results in time-space domain are obtained through the fast Fourier transform (FFT). Train speed and degree of saturation are mainly analyzed as important factor influencing ground vibration and excess pore water pressure. The results indicate that, at the track center, the vibration displacement amplitude increases significantly when the ground changes from near saturated (Sr = 99%) to fully saturated state. Also, the acceleration amplitude of unsaturated ground is larger and it decreases more rapidly with time than its counterparts for the scenarios of the saturated ground subjected to the train loading at the same speed. The development of excess pore water pressure of the unsaturated ground at the track center prevails in the shallow depth (0 ~ 4.5 m), and the peak value appears at about 1.8 m beneath ground surface. The pore water pressure decreases as the degree of saturation decreases.