Abstract:

Experiments on sound propagation in small-scale tunnels with a branch have been carried out from the viewpoint of safe and rapid information transmission underground. The influences of intersection angles and acoustical properties of inner walls of the tunnels on sound propagation were examined in previous studies [J. Acoust. Soc. Am. 100, 2567 (1996)]. In the present work, sound propagation in a full-scale underground tunnel with a branch is considered. The experimental tunnels are supported by iron frames and concrete lagging, and the cross sections are arch shaped with an area of 4.2 m[sup 2]. Experimental results indicate influences of the intersection on propagation attenuation at a frequency of around 200 Hz. Whole tendencies of sound attenuation are also affected by relative arrangements of sound source and receivers, and sound attenuates more at the receivers, which are out of sight from the source than for those in sight. For the purpose of the sound-field estimations, the characteristics of sound propagation are examined by numerical calculations using both an analogy with a resonant silencer with a branch and an image source model at the receivers, which are out of sight. Results of the numerical calculations relatively agree with the experimental results.