Abstract Summary
Trains will generate vibrations in the ground that will propagate to the buildings and radiated noise inside lodgings. Less known is the fact that the free surface will act as an infinite baffle radiating noise. This contribution is here studied. In order to quantify this effect, an existing 2.5D FEM/BEM model is completed. The free surface velocity field is used by means of a Rayleigh integration to compute the sound pressure levels radiated above ground. It uses the Green function above an infinite horizontal plane. The presence of buildings can be introduced by deriving an appropriate Green function based on a geometrical approach. A practical case has been used to compare predicted noise levels near an existing railway track and shows that the model recovers the low frequency emergence measured below 125 Hz. According to the calculations, the estimated ground-borne sound radiated is dominant at low frequencies and otherwise rather negligible compared to the sound directly emitted by the train/track system. Moreover, a small parametric study performed using a 2D source (vehicle and tracks) model coupled to the same ground model shows that the ground-borne sound radiated is ground dependent. The transmission of the noise component through windows has been compared to ground borne noise and found to be dominant, again, at low frequencies. Therefore, the ground should be considered as a separate sound source when dealing with railway sound and should be added to the other known sources (track and vehicle components).
