Propagation of Vibration from Rail Tunnels: Comparison Results for Two Ground Types

Detailed measurements of vibration transmission from an underground rail line in Sydney and a line in a deep cutting in Perth have recently been conducted. The propagation characteristics of these two ground types are very different, and neither fits comfortably with standard theoretical models of vibration transmission through a uniform ground. In Sydney, the results can generally be modelled as a vibration source slightly larger than the tunnel floor, propagating into a uniform medium, but with an attenuation rate which is much higher than expected for sandstone or similar rock. The additional attenuation may well be due to scattering from inhomogeneities in the rock, and hence may differ significantly between locations. In Perth, the only successful model is of two-dimensional propagation in a medium with almost no attenuation at low frequencies. These results emphasise the importance of on-site measurements in predicting vibration and structureborne noise levels from rail tunnels.