Mechanisms And Countermeasures Of Vibration Isolation And Damping In Urban Rail Transit

With the development of the urban rail transit, the vibration and sound caused by rail transit is becoming a serious environmental hazard that cannot be neglected, and the noise and vibration reducing measure becomes one of the hottest research topics. In this paper, the generation mechanism and spectrum characteristics of the excitation is analyzed and concluded. The vertical excitation of the urban rail transit is simulated based on compound excitation method, and mechanisms of vibration countermeasures are deeply analyzed, including floating slab track, wave barrier, and a new vibration damping system. The main content of this study is as follow:1. The generation mechanism and spectrum characteristics of the excitation are systematically analyzed. Resolution models of excitations generated by different mechanisms are summarized. The responses of the track are resolved in time domain and frequency domain respectively. On the basis of the above work, compound excitation method is proposed. Based on the analysis the effect of excitations on spectrum characteristics and vertical response and comparison the vibration responses of different frequency in track-tunnel-soil, the excitations that have obvious influence are filtrated. By superimposing the selected excitations, the compound excitation of the urban rail transit system under time domain is obtained.2. Floating slab track is cataloged as continuous cast-in-place floating slab track and discontinuous pre-cast floating slab track according to the construction method and length. These tow kinds of floating slab tracks are respectively simulated by continuous beam model and discrete beam model. Based on the theory of the Euler-Bernoulli beam and Timoshenko beam, the double continuous Euler-Bernoulli beam model and double discrete Timoshenko model are proposed, and the resolution model for double discrete Euler-Bernoulli beam and double continuous Timoshenko model are . The dispersion curve of the model is resolved in wavenumber-frequency domain by Fourier transformation, and the spectrum characteristic of the floating slab track structure is analyzed. The system response in space-time domain is obtained by contour integral and inverse Fourier transformation. The precise of the calculating is compared between double Euler-Bernoulli beam and Timoshenko beam, and the structure characteristic and damping effect of the continuous cast-in-place floating slab track and discontinuous pre-cast floating slab track are evaluated.3. The three-dimensional finite element model for floating slab track is established, and the effects of the dimensional parameters and dynamic parameters on dynamical characteristic of the floating slab are investigated. The dispersion characteristics of one-dimensional model and two- dimensional model of floating slab track are compared, and analysed the dispersion equations of rail-track-tunnel systematically.4. Based on the computing results of the finite element model, the vibration isolation effect on the low frequency vibration of the rail transit caused by trench is analyzed, and the effect of the depth of the trench, the distance between trench and vibration source, and frequency of vibration source on vibration isolation efficiency is discussed.5. A new vibration damping system -"Excitation Transmission Pile"system, can transfer the vibration induced by train to the bottom of the pile via track, and meanwhile, the bottom of the peg becomes the new vibration source, transferring the vibration to deep soil, reducing the ground vibration. The new vibration damping system can reduce vibration economically and reasonably. The numerical model of the"train-track slab-pile-soil layer"is established, and the vibration performance of the"Excitation Transmission Pile"system is systematically evaluated by parameter analysis.