Study On Tunnel Acoustic Design Based On Noise Annoyance

With the rapid development of urban tunnels construction,noise pollution in tunnels has became a problem that can not be ignored.In order to evaluate and optimize acoustical environment in tunnels scientifically,Zizhi tunnel in Hangzhou（composed of three types of tunnels:rectangular unidirectional two-lanes tunnel,circular arch unidirectional two-lanes and three-lanes tunnels）was taken as an example in this study.The noise characteristics and reverberation times(T₃₀)in tunnels were measured and analyzed.Noise samples sampled in tunnels were used to calculate noise annoyance in different types of tunnels based on improved Zwicker psychoacoustic annoyance model.By comparing reverberation times measured by reverse integration method with that obtained by ODEON,reasonability of simulation models were verified.Based on simulation model,influences on noise reduction effects from cross section shapes of tunnels,types and distributions of sound absorption panels on the side wall and ground materials were analyzed quantitatively.The results showed that T₃₀（4.4 s）in the rectangular two-lanes tunnel was higher than T₃₀（3.7 s and 3.1 s）in the circular arch two-lanes tunnel and three-lanes tunnel,which was related to that average free path of reflected sound propagation in rectangular tunnel was larger than that in circular arch tunnels.Psychoacoustic annoyances in three types of tunnels rank from big to small were rectangular two-lanes tunnel,circular arch two-lanes and circular arch three-lanes,which was related to that loudness in rectangular tunnel was higher than that in circular arch tunnel 17.96%～39.68%,roughness in rectangular tunnel was higher than that in circular arch tunnel 11.92%～29.83%,sharpness in rectangular tunnel was higher than that in circular arch tunnel 8.84%～13.75%.If sound absorption panels with vertical net height of 3 m were installed on the side wall of circular arch three-lanes tunnels,among four schemes（sound absorption panels were laid at 0.0 m,0.5 m,1.0 m and 1.5 m above the ground,respectively）,the noise reduction effects of these schemes were ranked from high to low as 1.0 m,1.5 m,0.5 m and 0.0 m.If sound absorption panels with same size（width 2.0 m×height 3.0 m）were laid periodically at 1.0 m above the ground along the longitudinal tunnel,in three types of schemes with periodic intervals of 1.0 m,3.0 m and 5.0 m,the noise level at concerned points in the scheme of 1.0 m interval will be 1.2 d B and 2.3 d B lower than that the schemes of 3.0 m and 5.0 m intervals,respectively.Annoyance can evaluate comprehensive perception of human body’s from noise nicely.In traditional noise control projects,noise control measures or schemes were usually optimized according to the reduction of A-weighted sound pressure level,which could not optimize control measures or schemes from noise annoyance improvement degree.In order to further optimize cross section shapes of tunnels and sound absorption schemes from annoyance improvement degree,as a case study,different types of sound absorption panels were installed on the side wall of rectangular and circular arch tunnels in simulation,and sound samples at concerned points（20 m,60 m and 100 m away from the tunnel entrance）were obtained after taking sound absorption schemes through the auralisation function of ODEON software.Based on noise subjective evaluation experiments,annoyance improvement degree in tunnels caused by cross section shapes of tunnels and sound absorption panels were quantitatively analyzed.Results showed that annoyances at different concern points in the rectangular two-lanes tunnel were higher than that in the circular arch two-lanes tunnel and three-lanes tunnel.This experimental result was consistent with the calculation result of psychoacoustic annoyance.Noise reduction effects from different kinds of sound absorption panels installed on the side wall of tunnel were ranked from high to low as follows:FC perforated panel（FC-PP）,CEMCOM sound-activated high-efficiency panel（CEMCOM-SHP）,ceramic foam panel（C-FP）,WHB inorganic foaming particle panel（WHB-IFP）and cement fiber panel.The noise annoyance improvement degree induced by different types of sound absorption panels at concern points were different.Average annoyance at concern points with different distance away from tunnel entrance were ranked from small to large as follows:CEMCOM-SHP,FC-PP,WHB-IFP,C-FP,and cement fiber panel in the rectangular two-lanes tunnel,and WHB-IFP,FC-PP,CEMCOM-SHP,C-FP,and cement fiber panel in the circular arch three-lanes tunnel.It can be seen that the sequencing of A-weighted sound pressure level reduction was inconsistent with that of annoyance improvement degree.In order to further improve acoustical environment in tunnels,sound absorption schemes in tunnels should be optimized and selected based on annoyance improvement degree.