[Key Information] Preliminary Results of Research on Noise/Vibration Source Intensity in Urban Rail Transit

To improve the scientific nature of urban rail transit environmental management, the Environmental Engineering Assessment Center of the Ministry of Ecology and Environment, in conjunction with several design institutes, has been conducting research on the intensity of urban rail transit noise and vibration sources and the effectiveness of vibration reduction and noise reduction measures under different boundary conditions in cities such as Fuzhou, Hangzhou, Suzhou, Guangzhou, Nanchang, Jinan, Nanjing, Shenzhen, Wuhan, and Shanghai since 2021. The research results are now compiled for reference by relevant units across the country in their related work.

I. Recommendations for Noise Source Intensity Values ​​of Elevated Urban Rail Transit Lines

Tests were conducted at approximately 50 noise source intensity points on elevated lines, resulting in approximately 500 measured data points. Recommendations for noise source intensity values ​​on urban rail transit elevated lines are provided for different vehicle types and speeds, as detailed in Table 1.

Studies have found that, in addition to the influencing factors indicated in the "Technical Guidelines for Environmental Impact Assessment of Urban Rail Transit" (HJ453-2018), the noise source intensity of elevated lines is also related to factors such as bridge structure, bridge quality, and the noise reduction capability of the vehicle itself. The selection of source intensity needs to be combined with the actual engineering situation.

II. Recommendations for Vibration Source Intensity Values ​​in Urban Rail Transit Underground Lines

Tests were conducted at approximately 180 vibration source intensity points of underground lines, and a total of about 16,000 measured data points were obtained. Recommendations for vibration source intensity values ​​of urban rail transit underground lines are given for different geological conditions, vehicle types, and vehicle speeds, as detailed in Table 2.

Studies have found that the vibration source intensity of underground lines is related to factors such as geological conditions, tunnel structure and form, construction methods (shield tunneling, cut-and-cover, mining), shield diameter and segment quality, and the selection of source intensity needs to be combined with the actual project.

III. Recommendations for the Noise Reduction Effect of Sound Barriers on Elevated Urban Rail Transit Lines

The effectiveness of a sound barrier can be obtained by comparing the noise monitoring values ​​in the sound shadow zone of the sound barrier (receiving point monitoring value) with the noise monitoring values ​​at the source intensity points without a sound barrier or the noise monitoring values ​​in the sound illumination zone of the sound barrier (reference point monitoring value). Due to limitations in actual testing conditions, the noise reduction effect tests of sound barriers in 10 cities, including Fuzhou, have primarily focused on monitoring the sound shadow zone at a location 7.5 meters from the centerline of the outer rail, at the same height as the rail surface, i.e., the receiving point in Figure 1. For vertical sound barriers, the reference point is mainly set at a position no less than 1 meter above the barrier. In practice, monitoring points at different distances from the centerline of the outer rail and at different vertical heights can be selected according to research needs to analyze the actual noise reduction effect of the sound barrier on sensitive targets at different distances and heights along the line.

We analyzed approximately 900 data points from over 60 measured cross-sections of sound barriers and provided recommendations for determining the noise reduction effect of sound barriers, as detailed in Table 3.

The noise reduction effect of a sound barrier is affected not only by the type of sound barrier, but also by factors such as the material of the sound barrier and the quality of its construction. When selecting the noise reduction effect value of a sound barrier, it should be further combined with the actual situation of the project.

IV. Recommendations for Evaluating the Effectiveness of Vibration Reduction Measures for Underground Urban Rail Transit Lines

The effectiveness of vibration reduction measures for urban rail transit is evaluated by comparing the difference between the same foundation reference point or analog reference point under the vibration reduction and non-vibration reduction states of the tunnel wall. The evaluation metric should be the maximum Z-level vibration during the train passage period, VLZmax, and the relative insertion loss ΔVLZmax of the Z-level vibration reduction measures should be given.

The track conditions (including geological conditions, wheel-rail conditions, track irregularities, rail surface condition, tunnel type, etc.), rolling stock, and operating conditions of the proposed and control sections should be the same or similar. The distance between the proposed and control sections should preferably be greater than the length of one train. The distance between the proposed section and the boundary of the proposed measure should preferably be greater than half the length of a train. If these conditions are not met, the midpoint of the track vibration reduction measures for that section should be selected.

The location of the measuring points for the basic reference points or analog reference points should comply with the relevant requirements of HJ 453-2018 for the selection of vibration source strength measuring points. At the same time, it is advisable to arrange measuring points on the rails and track bed as references.

Based on recent experience in urban rail transit environmental management, the research team categorized vibration reduction measures, such as double-layer nonlinear vibration damping fasteners and Lord fasteners, as medium-level vibration reduction measures; trapezoidal sleepers and rubber floating slab track beds as high-level vibration reduction measures; and steel spring floating slab track beds as special-level vibration reduction measures. Approximately 33,000 data points from nearly 190 sets of measured cross-sections of different types of vibration reduction measures were analyzed, and recommendations for the vibration reduction effect of different levels of measures are provided, as detailed in Table 4.

In addition to being related to the level of the measure, vibration reduction measures for underground lines are also related to many other factors such as geological conditions, track joint treatment, turnout conditions, project implementation quality, and the health status of the track and vibration reduction measures. When selecting the effective value of vibration reduction measures, it is necessary to further consider the actual conditions.

Source: Environmental Engineering Assessment Center, Ministry of Ecology and Environment. Please contact us to delete if there is any infringement.