Analyses of wave field from high-speed train on viaduct at shallow/deep soft grounds

In this paper, based on field measurements for the passage of the Shinkansen high speed trains on viaducts, the author reports the induced ground vibration features at distinctly different sites: one site is characterized by a deep soft soil and the other by a shallow soft soil both of which lie on stiff bottom. The conventional vibration assessment is normally addressed to the vibration levels based on acceleration maxima. However, in view of the vibration reception by nearby residents, firstly, a detailed investigation is attempted on the recorded time histories and on their Fourier spectra, locating the so-called low frequency vibration generation at the former site and such vibration impediment at the latter site. Then, theoretical consideration is to clarify the Shinkansen-train induced ground vibrations from a viaduct. The characterization based on the wave theory using the thin layer method reveals that, depending on the depth of surface layer, the ground-borne vibration is of significantly low frequency wave modes of dispersive propagation when it is deep or it makes the wave modes shifted towards higher frequency range when it is shallow. This finding makes an important element to better predict and assess vibration level and to develop barriers against it for mitigation.