Study On Ground Vibrations Induced By Subway Train And Vibration Isolation Of Floating Slab Track

With the development of the railway traffic, a lot of new problems such as environmental vibrations and uneven settlement of foundation have appeared. The vibrations caused by railway traffic have annoyed inhabitants’normal lives which live alongside railway lines. And it also affects the normal operation of some sensitive equipment nearby and may damage some historical buildings which cannot bear strong vibrations. Operation of railway for a long time may lead to uneven settlement of foundation, which will make the vibrations caused by railway traffic much stronger. So the vibrations caused by railway traffic and uneven settlement of foundation attract more and more scholars’attention.This thesis first applied the gradually damped artificial boundary into the2.5finite element method. By calculating the solution of a dynamic rectangular load moving inside a soil stratum and comparing to a semi-analytical solution, the accuracy of present method in analyzing vibrations under quasi static and dynamic loadings is verified.Then this thesis analyzed the vibrations of the ground and tunnel structure caused by a single moving load and a moving train load, in which the train load is considered by a constant load or an oscillatory load. Several observation points both on ground surface and inside ground are picked to inspect this problem. After analysis, conclusions can be obtained that the speed and the vibration frequency of the moving train loads have a great effect on the ground responses. The wave motions at the ground surface are confined to a narrow zone under pseudo-static moving train loads without a vibration frequency, and are found in a much broader zone under the moving train loads with low frequency. But with the increasing of the vibration frequency, the wave propagation zone at the ground surface becomes narrower.In order to simulate the vibrations caused by railway traffic more realistically, the track irregularity is taken into account, and the train is coupled to the track. In this model, a quarter car model moving on a rail surface with a cosine irregularity is adopted to calculate the wheel/rail contact force. In this part, the effect of the cosine irregularity’s wavelength and amplitude, the tunnel thickness and tunnel depth to the vibrations caused by trains are analyzed. After analysis, conclusions can be obtained that the tunnel thickness has little influence to the vibration, while the effect of tunnel depth, the cosine irregularity’s wavelength and amplitude to the vibration is related to the train speed.In this thesis, the vibration isolation of the floating slab track is also studied. In this analysis model, the double rails and slab are represented in the model by Euler-Bernoulli beam. To simplify the analysis model, both the fasteners supporting the rails and the slab bearings supporting the slab are homogenized as continuously distributed springs along the tunnel. The dynamic stiffness matrix of the track can be added to the2.5finite model through the interface nodes between the track and tunnel invert. In this part, the isolation of the floating slab is first analyzed. Then the soil and tunnel structure parameters, the track parameters (springs’stiffness and slab mass unit meter) and the irregularity parameters (wavelength and amplitude) analysis are conducted.In order to consider the irregularity more realistically, this thesis brings in the power spectral density function of the track irregularity in American. The power spectral density function can be converted into the real irregularity in space domain through the trigonometric series method. Then the real irregularity can be regarded as a series of cosine irregularities. By adding all the wheel/rail contact forces under each cosine irregularity together, we can obtain the real wheel/rail contact force under realistic irregularity and then the vibrations can be calculated. In this part, two different situations are considered:high speed railway and subway, and in each situation, different smoothness of the track and different train speeds are considered.