Research On Assessment Of Fourth Power Vibration Dose Value In Environmental Vibration Induced By Trains

Rail transit which brings more convenience to the citizens has been widely used in our country. However, with the rapid development of railway engineering construction, the environmental problems caused by railway vibration emerged and becomes more and more serious. The current evaluation standard of railway vibration in our country employs the largest Z vibration level as the assessment value, which will underestimate the negative influence of environmental vibration on human comfort under three conditions:the crest factor is greater than 9 (ISO2631-1:1997) or greater than 6 (BS6841:1987); intermittent vibration and occasional shock vibration when the crest factor is not more than 9 (or 6) and the transient vibration. However, the rail transit vibration is always intermittent and long-term. The railway traffic is increasingly busy today and the capacity of some railway lines, especially subway and high-speed rail lines is more than 30 times everyday. The residents complain more about the frequent vibration. However, the largest Z vibration level is lack of considerations about vibration number and also the duration of the vibration. Therefore, in this paper, the fourth power vibration dose value (VDV) was empolyed as an additional evaluation method to make up the above defects of the existing evaluation standards on railway environmental vibration. Moreover, the VDV method is more sensitive to the vibration peak on the basis of the fourth power.Based on the measured line filling embankment and bridge section analysis, the results were shown as follows:(1)The number of the trains passing through or the total time of environmental vibration and its distribution should be taken into consideration in the evaluation of railway environmental vibration.(2) For the irrigation line embankment and bridge section of Cheng Guan line, the vibration acceleration level accorded with the existing provisions when only a train passed through. The peak factor within the continuous vibration time lied between 3 to 6 and the peak factor obtained in the bridge section was higher than that obtained in the irrigation line embankment. Moreover, these data could be adopted to calculate the VDV value.(3) Taking the real environmental vibration of the irrigation line embankment into account, the difference among the vibration accelerometer temporarily effective values of X, Y and also Z direction was small. The intensity decayed along with the increase of distance and the decay speed of the intensity in X direction was greater than that in Ydirection.(4) Taking the real environmental vibration of the bridge section into account, the vibration accelerometer temporarily effective values of X, Y direction were greater than that of Z direction in close-ups and so was the decay rate. Within 40 m, vibration attenuation in Y direction was the fastest. The horizontal direction cannot be ignored for the evaluation of railway environmental vibration.(5) The VDV value accumulated rapidly along with the increase of the number of the trains passing through and the vibration duration. Moreover, it was more sensitive to the peak value. And thus, applying the fourth power vibration dose to the current railway environmental vibration evaluation method in our country, the shortcomings of the opening times and the total time can be compensated and the peak value can be highlighted.