A model for ground vibration from railway tunnels

Trains give rise to vibration which propagates through the ground to nearby buildings. At low frequencies (about 4–80 Hz) ‘whole body’ vibration is generated which may be felt, while at higher frequencies (about 30–200 Hz) a rumbling sound is radiated from vibrating walls and floors into the rooms of buildings. Low-frequency vibration is primarily associated with heavy axle-load freight trains running on lines on the ground surface. Structure-borne noise is most often perceptible from trains running in cut-and-cover or bored tunnels where the direct airborne sound of the train is absent at the receiver. For either phenomenon, numerical models for the transmission of vibration through the ground are required to predict the effect of structural alterations to cuttings, embankments and tunnels, or of foundation engineering. To address this, a coupled boundary element/finite element model for vibration propagation has been developed. By restricting analysis to two dimensions, trend analysis can be performed with models that require much lower computing resources than would be required for three dimensions. Here the method is applied to study the effect of design alterations of a bored tunnel and a cut-and-cover tunnel on the transmission of vibration for a frequency range up to 200 Hz.