Numerical simulation study of ground vibrations using forces from wheels of a running high-speed train

A 3-D viscoelastic finite difference method (FDM) was adopted to study the mechanism of ground vibrations induced by a high-speed train. Time-series data of the forces acting on the railroad were observed from the wheels of a running Shinkansen train in Japan and were used to develop a realistic source function as an input to numerical simulations for a single wheel. This is because the measured forces include suitable frequency components. A 3-D numerical model of the embankment of the railroad was designed to mimic a test field site for which borehole logging data were available. Simple analytical discussions concluded that a rail length of 120 m and a grid spacing of 0.25 m were acceptable for stable FDM simulations without numerical dispersion, and a model with about 32 million grid points was adopted for this study. A staggered-grid FDM with fourth-order accuracy in space was used for the numerical simulations. Finally, the simulated ground vibration was compared with the observed vibrations at the test site. The simulated ground vibrations closely resembled the observed ones. At the test site, the quality factor (Q) was not observed experimentally; however, the best match with field data was realized by assuming Q=5–50.