Measured Analysis of Vibration Source Strength in Metro Tunnels Influenced by Vehicle Condition Factors
This study focuses on a straight-line section of a subway line to analyze the factors influencing the vibration source strength in subway tunnels.Vehicle-induced vibration signals and velocity signals were collected synchronously,and the time-domain and frequency-domain characteristics of all-day test samples were statistically analyzed.The results showed that during peak hours in the morning and evening,the vibration response inside the tunnel may not be completely maximized,and the degree of dispersion of the vibration source intensity is directly related to the vehicle state.The study found an average difference of 6.7 dB in the VLZ of the tunnel wall measurement points caused by Vi and V2 vehicles.Using more than 40 sets of test samples to calculate the vibration source intensity yielded results closer to the daily sample mean.The main frequency of tunnel vibration caused by the wheel-rail system shifts with changes in vehicle speed.A strong linear positive correlation was observed between vehicle speed and the vibration acceleration levels of the track bed and tunnel wall.Specifically,for every 10 km/h increase in vehicle speed,the vibration increases by about 1.7 dB and 2.6 dB,respectively.When the speed difference is within 10 km/h,the vibration source intensity changes within 1 dB;when the speed difference is between 10～20 km/h,the increase is about 1.5～2.2 dB.The coefficient of speed-corrected CV was calculated to be 18.5,aligning closely with the coefficient used for train speed correction in the vibration prediction formula.Tunnel wall vibration was more discrete in the low-frequency band below 40 Hz,but this band contributed minimally to the source strength of vibration,accounting for 15.29％.The dominant frequency band was 50-63 Hz,contributing 59.55％to the source strength of vibration.These research findings can provide a reference for further refining the vibration prediction formula and offer a theoretical basis for improving the accuracy of metro tunnel source strength test results.
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