Prediction Research On Metro Traffic Induced Environmental Vibration Based On Measured Transfer Function

The influence of environmental vibration caused by subway traffic has become one of the bottleneck problems restricting the healthy and sustainable development of subway construction.Based on the influence of subway traffic vibration on precision instruments of a key Laboratory,this paper develops a method to predict ground vibration response based on tunnel-stratum transfer function obtained from in-situ hammer excitation experiment in tunnel.The frequency-domain excitation forces acting on the tunnel base are calculated by using the train-track coupling analytical model,and the calculated frequency-domain excitation forces and measured transfer functions are used to predict the vibration responses in the buildings caused by subway traffic.According to the prediction results,the vibration influence on precision instrument in laboratory is evaluated,which provides reference for vibration reduction and isolation measures of subway traffic.The main contents and results are as follows:(1)The theoretical system of influence prediction of vibration based on transfer function is sorted out,and a method of prediction of subway traffic vibration based on measured transfer function in tunnel is developed.The prediction problem of subway environmental vibration is decoupled into two parts: one is to solve the frequency domain excitation force sequence of tunnel basement by using the train-track coupling analytical model;The second method is to carry out field hammer test in tunnel to obtain the transfer function sequence of tunnel-soil system.The vibration response at the measurement point on the surface or in the building can be obtained by multiplying and stacking the excitation force sequence and the transfer function sequence in the complex domain.This prediction method in frequency domain for the whole process,the train operation caused by different positions of the tunnel basal exciting force and the transfer function of amplitude and phase are taken into consideration,and as a result of the measured transfer function can reflect the specific point of the tunnel-soil system vibration transfer characteristics,so this method can accurately predict the subway train operation caused by the vibration response of the environment.(2)By changing the calculation conditions of the train-track coupling analytical model,the excitation forces in frequency domain for tunnel basement under different vehicle speeds and different track forms were obtained.Through the prediction way,the influence laws of different vehicle speeds and track forms on environmental vibration were predicted.The results show that the vibration response trends of the same measurement point on the ground surface are similar under different vehicle speeds.The train speed has a significant influence on the vibration response of the measurement point on the ground surface and inside the building.The higher the vehicle speed is,the greater the vibration response is.For common integral track bed,the vibration caused by subway train operation exceeds the vibration limit requirements of laboratory precision instruments in most frequency bands.The use of steel spring floating plate track can ensure that the ambient vibration above 20 Hz caused by subway train operation meets the vibration limit requirements of precision instruments,but the vibration below 20 Hz still exceeds the vibration limit requirements of precision instruments.