Research On Environmental Noise Characteristics Of Elevated Section Of Urban Express Line

With the continuous development of cities,rail transit lines will become more and more dense,and it will become increasingly difficult to avoid environmental noise sensitive points in the design of new lines.Due to its low land acquisition and demolition,simple construction,short construction period,low cost,and low operation and maintenance costs,the elevated line accounts for a large proportion of the urban rail transit lines connecting the suburbs,so the environmental noise around the elevated section People are paying more and more attention.This paper systematically studied the relevant data of urban rail transit noise at home and abroad.Through field measurement of the environmental noise in the operation of the elevated section of Chengdu Metro Line 18,it analyzed the characteristics of the elevated section noise and the attenuation law in the horizontal direction,and discussed the applicable range of the existing environmental noise prediction formula.The main contents and conclusions of this paper are as follows:1.Through the post-processing of the collected noise signals,the equivalent continuous A sound level during the passing time of the train at each measuring point is obtained.The noise source intensity of the elevated section ranges from 92.6d B(A)to 93.3d B(A),with an average value of 93.1d B(A),the 95% confidence interval is [92.9 d B(A),93.2 d B(A)];as the distance increases,the horizontal noise first increases and then decreases.The train speed is 138.3km/ The equivalent continuous A sound level of each measuring point when h passed is greater than the A sound level when the train passed at a speed of 128.7km/h.The empirical formula of noise attenuation is fitted by the measured data.2.When the train passes,the fluctuation of sound pressure generated when the train head arrives at the measuring point is larger than that when the train tail leaves.The amplitude of sound pressure tends to decrease with the increase of the distance from the center line of the near orbit,and the rate of attenuation decreases with the increase of the distance.3.The main frequency of the noise source in the overhead section is in the broadband range of 250Hz～5000Hz,and the maximum band sound pressure level appears at 1250 Hz.The main frequency of horizontal noise is in the frequency range of 250Hz～2000Hz,and the frequency band of noise attenuation with distance is mainly in the range of 80Hz～400Hz.In the acoustic shadow region(7.5m～15m),the frequency band of 125Hz～200Hz is mainly affected by the speed,and at 30 m,the speed has an effect in all frequency bands.In the range of 30m～60m,the main frequency bands affected by speed are 63Hz～200Hz and315Hz～5000Hz.4.The comparison of the existing environmental noise prediction formula on the horizontal noise prediction result and the actual measurement result shows that the actual measurement value of each point is less than the predicted value,and the prediction effect is better.It also predicts the impact of the operating noise of the elevated section of Chengdu Metro Line 18 on the acoustic environment quality along the line,and proposes planning recommendations.