Experimental Study On Ambient Noise Characteristics And Control Methods On Sinking Metro Depot

In recent years,the new structural form of sinking metro depot has appeared in urban subway projects in my country,which has better solved the problem of comprehensive and efficient development and utilization of land resources in the depot.However,due to the need for ventilation,the 24-hour uninterrupted operation of a large number of ventilation equipment in the sinking metro depot has generated serious equipment noise.In addition to the train operation noise and workshop maintenance noise,the depot employees continue to be exposed to a bad sound environment.Therefore,it is urgent and necessary to study the characteristics and propagation laws of environmental noise in the sunken vehicle depot and its noise control methods.Based on the project of Shihu metro depot of Guangzhou metro line 14,this paper first adopts the method of questionnaire survey and field test to carry out investigation and test in the space under the cover,the ground above the cover and the adjacent buildings of the depot,and systematically studies the noise source,sound field characteristics and noise transmission law in the sinking metro depot.Furthermore,the numerical simulation method is used to simulate and analyze the influencing factors and rules of environmental noise by establishing the sound field model of the singking metro depot,so as to put forward countermeasures and suggestions for the design of the noise control method of the singking metro depot.The main conclusions are as follows:(1)The main noise sources in the sinking metro depot are ventilation system noise and train running noise,and the influence of maintenance noise and road traffic noise is relatively small;In the noise annoyance survey,88% of the respondents in the sinking metro depot were disturbed in language communication,and 95% of the respondents were annoyed by the noise.There was a serious noise impact in the depot,and the impact degree was higher than that in the ground depot.(2)Different noise evaluation standards should be adopted for the cover and under cover of sinking depot.According to the requirements of the "Code for design of noise control of industrial enterprises",the noise limit of 60 dB(A)is adopted in the office area and 85 dB(A)is used in the maintenance work area;The covered buildings are in line with the characteristics of class 2 area in "Standard for limit and measuring method of building vibration and secondary noise caused by urban rail transit",with the daytime limit of 41 dB(A)and the night limit of38 dB(A).(3)Field test results show that: The noise intensity in the office area exceeds the standard limit by 3～5dB,and closing the door can only reduce less than 1dB(A);The noise intensity in the corridor decays linearly,and the medium and high frequency decays quickly.The measuring point 9m away from the noise source has reached the standard limit;Through the NR curve evaluation,the mid-frequency noise around 1000 Hz brings the highest annoyance to people.The sound field in the maintenance room spreads around in the form of waves,and the overall noise attenuation amplitude is small;In the vertical direction,due to the simultaneous action of multiple sound sources,it exhibits the characteristics of attenuation from the middle to the two sides;The secondary structure noise intensity in the upper driver’s apartment does not meet the requirements of the environmental standard limit.Among them,the frequency range of16～250Hz exceeds the standard seriously,and it has obvious low-frequency characteristics.(4)The noise of the sinking depot maintenance garage can be effectively controlled and improved by changing the sound absorption material,sound absorption position,sound absorption area,and adjustment of the space layout.In the design of interface sound absorption,when low frequency sound absorption material is selected,the sound absorption position is in the middle of the ceiling and the sound absorption area is between 20-30% of the ceiling area,the noise reduction efficiency is the highest;In the design of the direction of the air outlet,the noise reduction effect is best when the air outlet faces the walls on both sides,but the included angle should not be too low,and the noise reduction effect should be balanced with the ventilation demand;In the design of the space structure,the width should be controlled at about24 m,which can effectively improve the acoustic environment of the vehicle section.