Research On Subway Sound Field And Noise Reduction Effect Of Erect And Reflective Noise Barrier

The subway noise has a great impact on the quality of urban residents' life,which is necessary to be solved.As an effective noise reduction method,the noise barrier has been widely used in the prevention and control of railway and highway noise.However,the subway noise is dominated by low-frequency noise,the noise reduction effect of the existing noise barrier is not ideal Aiming at the characteristics of subways noise,the structural parameters of noise barriers which are suitable for subways were researched.So that the noise reduction effects of noise barriers were enhanced,which has significance for improving the urban residents' life.Therefore,focusing on the noise characteristics of subway trains,this article conducted the following research:(1)Because the frequency spectrum and sound pressure level of the sound source can affect the noise reduction effect of the noise barrier,accurate subway noise information must be obtained before the research.This article selected the ground line of the Beijing Subway Line 13 to collect the noise signals at multiple points simultaneously.The free sound field was tested on a cross section of the line between Lishuiqiao Subway Station and Beiyuan Subway Station.The noise barrier sound field test was performed on a cross section of the line between Guangximen Subway Station and Liufang Subway Station.The equivalent sound pressure level,frequency spectrum,traffic noise index,noise pollution level,and acoustic exposure level collected at the measuring points were analyzed.(2)Based on the noise characteristics of subway trains obtained from the test and the finite element theory,a spatial model of subway noise barriers was established.The free sound field and noise barrier sound field were simulated respectively.The calculation frequency was based on one-third octave and test data.The calculation frequency range was 50Hz-160Hz,where the noise peak frequency is 160Hz.Comparing the calculation results with the test results,the reliability of the finite element method to calculate the insertion loss of the noise barrier was verified.The influence of the sound pressure level on the free sound field and the noise barrier sound field was studied.(3)Through changing the noise barrier height,the distance between the noise barrier and the sound source,and the sound absorption coefficient of the noise barrier's one side surface near the sound source,the influence rules of noise reduction effect(ie,the insertion loss value)and the ways to improve noise reduction was determined.In the test and simulation calculations,the following conclusions have been drawn:The noise spectrum of subways on the ground mainly concentrates in the frequency range of 50Hz?160Hz,and the peak frequency is 160Hz.When the height of the noise barrier increases,the proportion of the noise shadow area increases,the area whose noise is lower than the environmental noise limits in city also increases.The insertion loss value increases with height's increasing when the noise barrier is 3m away from the sound source,but the insertion loss changes little when the height higher than the critical height of 4.5m.With the distance between the noise barrier and the sound source increasing,the critical height decreases.The insertion loss of the noise barrier decreases with the increasing of the distance between the sound receiving point,but when the distance increases to 20m,the insertion loss value tends to increase,but the peak value is smaller than the peak in the region near the noise barrier.The insertion loss value is larger than 4dB in the distance of 1m?25m from the noise barrier,indicating that the approximate width of the sound shadow zone is 25m behind the noise barrier.With the increase of the sound absorption coefficient,the insertion loss value has a tendency of increasing first and then decreasing.The maximum insertion loss value is 12.0dB,when the sound absorption coefficient is about 0.65.Changing the material of the pavement has little effect on the insertion loss value,and it only has relatively obvious effect when the noise is below 200Hz.