Full-scale measurements for noise transmission in tunnels

Abstract

In many previous studies, energy-based methods are used to predict the attenuation of sound in long tunnels. However, these models do not address the interference effects of the sound fields generated by all image sources. A numerical model has been developed, in which the total sound field is computed by summing contributions from all image sources coherently. This numerical model also incorporates a correction term for calculating the atmospheric absorption of sound in air. To validate the numerical models in practical situations, two road traffic tunnels have been chosen for extensive measurements. The levels of the transmitted noise have been recorded in one-third octave band frequencies at various separations up to a maximum of 400 m. The predictions using the coherent model agree reasonably well with the measured data at all frequencies. The agreements between the field data and the theoretical predictions using the energy-based model are tolerable at high frequency, but less so at low frequency. In most cases, the predictions of the coherent model give the best results, with an accuracy to within 3 dB. On the other hand, the energy-based models are not able to predict the peaks and dips across the frequency spectra, the variance with the measurement results being up to 7 dB at low-frequency bands.