Analysis on the Variation Characteristics and Formation Mechanism of Environmental Vibration Level Caused by Metro Operation.

In order to analyze the variation characteristics and formation mechanism of environmental vibration caused by metro operation, field measurement of ground vibration and tunnel wall vibration are carried out along a metro line in Beijing. Vibration sample data of all trains in a whole day are analyzed statistically. And the main reasons for the discreteness of environmental vibration are summarized by comparing the vibration variety rules of different trains and different sections. The result shows as following. Firstly, the difference of vibration level at ground point can reach at most 14.6 dB, with a large degree of dispersion. Although the average value of twenty trains could meet the requirement of the standard prescribed limit, but there is still 30% ~ 50% of vibration values exceeding the standard prescribed limit. Secondly, the difference of vibration level at tunnel points reaches at most 22.1 dB, which is caused by the abnormal status of five vehicles in all trains on the day with the symptom of wheel irregularity. And the average value of maximum Z weighted vibration acceleration level (VLZ_max) at tunnel wall points caused by them is 90.6 dB. Thirdly, vibration level at tunnel wall points between different sections induced by thesame vehicle is changed notably. And there is an important correlation with vehicle status. When the wheel is out of roundness visibly, the vibration level difference between different sections is changed more significantly. The maximum noise level can reach 10.7 dB, which is twice of 'normal vehicle', indicating that the deterioration of wheel state and track state will further change the wheel-rail interaction and aggravate the environmental vibration level. In addition, after wheel reprofiled of abnormal vehicles, the vibration level at ground point close to building is effectively reduced and all vibration values are reduced to less than 70 dB. [ABSTRACT FROM AUTHOR]