Calculations of sound radiation associated with 'tunnel boom' from high-speed trains

This paper presents the results of the theoretical calculations of sound radiation from tunnel portals by air shock waves generated by high-speed trains travelling in underground tunnels. This phenomenon, also known as 'tunnel boom', is associated with very loud and sharp noise, similar to that of cannon shots. This noise may be very disturbing for local residents and wildlife. A simple analytical model has been developed to calculate the generated sound. The model takes into account the ground effect outside the tunnel and uses Rayleigh integral to calculate the sound pressure. The model can predict the acoustic frequency spectra and the waveforms generated at arbitrary distances and directions outside the exit tunnel portal. Numerical results have been produced for several selected tunnels in the UK located along the planned high speed railway route HS2 and identified as being capable of generating tunnel boom. Potential implications of these results are discussed, as well as possible mitigation measures.