Income Effect in the Railway Galleries

Noise pollution caused by underground railways is particularly felt in open sections close to tunnel entrances. This is due to the fact that acoustic emissions increase near tunnel entrances because of the reverberated field inside the tunnel (income effect); this effect contributes in a substantial way to noise pollution in the surrounding areas. Within reclamation projects, the acoustic impact on open sections close to tunnel entrances must be simulated. In order to characterize the acoustic source it is necessary to consider both direct emissions and the contribution from the reverberated field from inside the gallery. For this reason a simplified method has been introduced based on acoustic and dimensional characteristics of tunnels that allows to take the income effect into account by using an appropriate virtual source. Theoretical results have been confirmed by field measurements.