Research On Transfer Function Of Fixed-Point Impact Method Used For Metro Train-Induced Environmental Vibration Prediction

With the rapid development and large-scale construction of urban rail transit in China in recent years,the problems of train-induced environmental vibration have arisen as well,which makes an adverse impact on the living quality of residents and sensitive buildings with special functions near metro lines.The contradiction between the traininduced environmental vibration problem and the need of people’s awareness has become an obstacle to the continuous development of urban rail transit.Therefore,it is necessary to develop scientific and accurate prediction methods to meet the demands of various vibration sensitivity in different metro construction stages.As a type of precise prediction method which is applicable to the detailed evaluation stage,the transfer function method employs the impact excitation to measure the transfer function of soil layers of a tunnelsoil system.It has high prediction accuracy and can decrease the certainty of modelling the vibration propagation path.However,before the tunnel is constructed,the problem of the transfer function correction should be solved.Moreover,the feasibility and improvement methods of the completed tunnel still need to be further investigated due to some measurement difficulties,such as the admission conditions of excitation equipment.Accordingly,with the support by the National Natural Science Foundation of China "Research on the Impact of Metro Train-induced Vibration Environment on Uncertainty of Parameters Based on the Hybrid Prediction Method"(No.51978043),this thesis is centered with transfer function in the fixed point hammering load and implemented through a series of laboratory tests,theoretical deduction,analytic computation and so on.The main research work is as follows:(1)The experimental study on the mutual inversion of transfer function was carried out in the underground tunnel of the Laboratory of Track Vibration Abatement& Control of Beijing Jiaotong University.By comparing the difference of transfer functions under impact excitation load in the tunnel and on the ground surface,the applicability of the prediction method for "tunnel-soil" system was verified.(2)Based on the theoretical analysis approach,the thin layered method(TLM)was employed.The motion equation of the elastic half-space was deduced from the cylindrical coordinates to a solution of three-dimensional layered foundation displacement.The perfectly matched layers(PML)was applied in TLM,which could avoid the absorption of vibration wave at boundaries.(3)Based on the superposition principle with Volume Method(VM),the dynamic interaction model of tunnel-soil was established.With the TLM-PML method,the displacement frequency response function of the foundation soil around a tunnel was deduced.The calculation program of dynamic interaction analysis model of tunnel-soil was finished.The experimental results of the in-tunnel-excitation measurement and calculation results by TLM-VM-PML method were compared and analyzed,with which the accuracy of this method was proved for solving the dynamic interaction analysis of tunnel-soil system.(4)The TLM-VM-PML method was applied to solve the frequency domain correction function of a tunnel structure.The effect of tunnel buried depth,soil shear wave velocity and soil density on the correction function was discussed.In addition,the main range of the effect of tunnel structure on the ground vibrations were obtained.