A Study On The Effect On Environment Of Vibration Induced By Subway Train

With the rapid development of economy and gradual expansion of city size at home, urban rail transit is increasingly become the preferred strategy to solve the problem of urban traffic congestion. Because subway has some vantages in facilitate its efficient, safe and comfortable, small air pollution and other advantages, it has fast become a modern means of transport and has been rapid development. At the same time, the effect on environment of vibration induced by metro is increasingly becoming one of the issues of universal concern. A number of facts have proved that part of the subway lines had produced a great impact on the human body's physical and mental health, building structural safety and the normal use of precision instruments. Therefore, the pollution caused by the running of certain metro train can not be ignored. Researchs on metro-induced ground vibration propagation and the vibration response of structures for future subway construction and the vibration and noise reduction have very important significance.In this paper, through establish the three-dimensional finite element model based on the geological survey report of a city subway line, it numerical simulation and theoretical analysis to study the propagation of soft soil base subway vibration attenuation trends, and the impact of vibration on buildings. The paper focuses on the main content of the above, were analyzed systematically.The vibration of track structure caused by the running of certain metro train was simulated by using a continuous elastic double layers beam of track structure. Through using Fourier change method and mathematical software-MATLAB, the forces on tunnel floor produced by subway train were calculated, and which is applied to the three-dimensional simulation model to analyze the vibration propagation caused by subway.Using the simulation software-ANSYS, the tunnel-ground interaction 3D simulation model was established and the dynamical responses of ground surface under the train's moving load were simulated. The vibration responses of ground surface with different train speeds, different tunnel depths and different levels of track irregularity is analyz, and obtain some conclusions.The vibration level of ground surface induced by metro train decrease rapidly with an increase in the distance to the tunnel center and is amplified at a certain distance away from tunnel center. Which are mainly due to the combined effects of geological conditions, excitation frequency, tunnel depths etc. In the propagation process, High-frequency vibrations attenuate faster than the low-frequency vibrations.Metro vibration response exist a certain critical velocity, when the train speed is less than the critical value, higher train speed induces larger vibrations. Or else, higher train speed induces smaller vibrations.The vibration levels of different locations on ground surface are weakened with the increase of tunnel depth and enhanced with the reduction of level of track irregularity.The vertical vibration curve of double parallel tunnels is basically the same with single tunnel.The former slightly larger than the latter. The vibration levels are gradually weakened with the increase of distance between center lines of double tunnel. But due to a change of vibration rebound zone, vibrations of some locations are enhanced with the increase of distance.Using the finite element software-ANSYS, the tunnel-ground-building interaction 3D model was also established. The vibration characteristics of different floors of the building under the train's moving load with different train speeds, different tunnel depths and different distances to tunnel center were obtained. The vibration responses of building induced by the passing of certain subway train in general increase with the increase of floor, but little difference between each floor, showing movement as a whole. Higher train speed, smaller tunnel depth and shorter the distance between a building and tunnel all induce larger structural vibrations. But at a certain distance away from the tunnel center will appear the phenomenon of vibration rebound. With the slab thickness of building increases, the vibration responses of floor significantly decreased; the diameter of pile foundation also has an impact on vibrations, but very small.The Metro-induced vibration transmitted from the rail to track bed, and then spread to the tunnel structure, the vibration is gradually weakened, but the attenuation of vibration energy occurs mainly in the "Rail –Track bed" stage.