Research Of Environmental Vibration Generated By Unballasted Slab Track

For a long time the running speed of the train is relatively low in China, therefore, the railway induced environmental vibration is an area to which the research community has not paid enough attention. There are only limited researches were conducted, such as the preliminary theoretical analysis and the site measurement research alone the urban railway line. The environmental vibration researches under the conditions of high speed train or unballasted track were also few. At present, a complete theoretical analysis method, which is urgently needed to study the propagation and the influence factors of the train induced environmental vibration, develop economical and effective method for controlling the vibration. It is aimed to provide technical support for leap-forward development of Chinese railway.This thesis reviewed and analyzed the history and present status of the environmental vibration studying. Then, the comparatively perfect three-dimensional analytical and numerical models, which are suitable to the study of the environmental vibration on conditions of metro and embankment unballasted track lines were established. Influence factors of the train, the track, the subgrade, the tunnel, and the building structures are comprehensively considered in the model.Based on the solution of the track and the layered ground dynamic equations in wave-number domain, the analytic model of ground vibration caused by the slab track under the axle load is established. Viscous damping is used to describe the attenuation of the track vibration. Layered soil model can reflect the propagation of waves in the three-dimensional elastic medium. It's not necessary to consider the influence of the calculation domain border, which has little restriction on the model establishment. The interaction of the track and the ground is analyzed. When the train velocity is close to the Rayleigh wave speed of the soft ground, the response of the ground exhibits severe oscillations. The influence of the different axle load to the environment vibration is also discussed.Based on the vehicle-track coupling dynamic theory, a three dimensional train-track-ground coupling numerical model is developed to simulate the train induced ground vibration. The vertical plane model is established to simulate the considered vehicle and track. The track is meshed by the 4-node, 8-freedom composite beam finite element. The three-dimensional hexahedron finite element is used to mesh the calculation domain of the ground. Impedance and scattering characteristics of the calculation domain edges are simulated by three-dimensional visco-elastic artificial boundary. Interaction between the train and the track is achieved at the wheel/rail interfaces through wheel-rail force compatibility, which is described by the non-linear Hertzian theory. The nonlinear wheel-rail action force, the material's discontinuousness, and the complex geometrical configuration are considered in the model. The train length has no restriction for the computational domain. Both the train-track-ground-frame coupling environmental vibration model for embankment lines and the train-track-ground-tunnel-frame coupling environmental vibration model for metro lines were developed on the basis of the model above mentioned.The environmental vibration induced by the motor train unit passing through the embankment lines, was calculated by using of the numerical method. The main researches cover the following aspects, which are vibration characteristics analyzing of the ground surface and frame structure in the vicinity of the line, vibration control effects exploring of the unballasted track's dynamic parameters, Influence studying of the geometric and physical parameters of the vibration isolation trench. The results show that the ground vibration decreases with the distance to the track, according to the exponential formula. The vibration level could be decreased by thickening the slab and improving the elasticity of the rail fastening and adjustment layer. The vibration level could be decreasing about 8dB～10dB by opening isolation trench with the reasonable depth of 5m～7m.A numerical calculation model was derived to study the ground vibrations caused by metro trains. These are researches followed are the main contents of this work. The study concerned with the ground vibration characteristics around the circular tunnel, influences of the rail track structure, the tunnel depth and the ground elastic modulus, comparative analysis of the high-rise and the low-rise frame structure's vibration. The present results suggest that the train mainly inducing the low-frequency vertical vibrations of the ground surface, which are generally greater than the lateral vibration in the area vicinity to the central line of the turnnel. There exists a vibration amplifying zone in the distance of 20m～30m to the railway line. The maximum vibration value of the high-rise frame structure appears at its middle part, while as for the low-rise frame structure, maximum vibration value appears at its top. From the view of controlling environmental vibration, the tunnel depth should be more than 13m. These results provide essential reference for anti-vibration design of the high-speed railway building and the urban rail transit construction.