Investigation of saturation effects on vibrations of nearly saturated ground due to moving train loads using 2.5D FEM

An improved two-and-a-half dimensional finite element method (2.5D FEM) model is developed to predict ground-borne vibrations in coastal areas from passing high-speed trains (HSTs). The model treats the ground as nearly saturated layered half-space, and describes the pore water/air mixed fluid by the equivalent fluid approach. Reliability of the proposed model is verified by comparing with the field measurements for X-2000 train and published analytical solutions. On this basis, the ground vibrations and excess pore water pressure under different train speeds and on various soil cases are analyzed in detail. In particular, three kinds of water saturation are discussed to show the sensitivity of vibration responses to the minor change of saturation. Results show that the saturation would cause pronounced influence on vibration displacements and excess pore pressure, and a minor decrease in water saturation would lead to a much higher vibration displacement level and a big difference of excess pore pressure distribution along depth. The influence of saturation is dependent both on soil configurations and on train speeds. It is highlighted that the vibration level on coastal ground would be underestimated by using fully saturated model instead of the nearly saturated model.