Measures For Reducing Vibration On The Surrounding Environment Under Overlapping Tunnel Subway Loads

With the continuous economic development and the rapid growth of population,traffic is become very congested. Floor space has failed to meet people’s demands,people begin turning to the underground space. Subway will not only be very convenient for people, but also bring problems of vibration and noise. In this paper,taking the first section between line 2 and line 4 in Wu Han as the research object, using the finite element method in order to build a three-dimensional finite element model of ANSYS- four holes overlapping tunnels, analyze vibration impact and measures for reducing vibration on the surrounding environment.1) The propagation law of vibration wave in the soil is summarized, and reasonable subway vibration loading is reasonably selected. This paper briefly introduces the finite element dynamics method of vibration problems.2) In the free field, to create a three-dimensional finite element model of ANSYS-four-holes overlapping tunnel, model size and unit type, soil material, integral time step,damping coefficient and viscoelastic artificial boundary are reasonably selected.Artificial excitation force is applied to the 2L tunnel to analyze vibration law of measuring points on the ground and underground. ⑴ The farther away from the vibration source is, the smaller vibration intensity of measuring points on the ground are.⑵ At the same depth, the closer to the vibration source is, the greater vibration amplitude of measuring points underground changes; On the contrary, the farther away from the vibration source is, the smaller changes of amplitude of measuring points underground is; After a certain distance, horizontal distance increasing, although changes of amplitude of the vibration is reduced, but it is not obvious. In four-holes overlapping tunnel, different combinations of the train(mainly two combination trains)are running, causing vibration law of measuring points on the ground. ⑴ As the depth of vibration source increases, the vibration intensity of measuring points on the ground decreases. ⑵Along with horizontal distance of vibration source increasing, the vibration intensity of measuring points on the ground decreases. ⑶ Compared with the change of horizontal distance, the subway vibration intensity affected by the depth of the vibration source is stronger.3) From the perspective of the location, width, depth and stiffness of thebarrier,analyze how to reduce or prevent the amplitude of the vibration of underground continuous concrete wall. ⑴ After setting the barrier, vibration intensity of measuring points near front of barrier increase, which is the closer to barrier, the more increases;vibration intensity of measuring points after barrier decreases, which is the closer to barrier, the more decreases. ⑵ When the position, depth and stiffness of the barrier remain unchanged and width increases, vibration intensity of measuring point on the ground decreases and the isolation effect is more obvious. ⑶ When the position, width and stiffness of the barrier remain unchanged and depth increases, vibration intensity of measuring point on the ground decreases and the isolation effect is more obvious; Over the depth of the vibration source, the depth of the barrier increasing, although the effect is increased, but it is not obvious. ⑷ The isolation effect of empty trench is best,followed by foam board, and finally concrete underground continuous wall.