Study On Isolation Effect And Mechanism Of The Non-continuous Vibration Isolation Barrier For High-speed Railway

High-speed railway has the advantages of large passenger capacity and high punctuality ratio and it has gradually become a popular trip and transportation model for modern people.The development of high-speed railway in China attracts worldwide attention.However,the environmental vibration and noise pollution along the railway have inevitably aggravated with the increase of train speed,transportation capacity and transport density.This has a great influence on the physical condition of residents,the normal use of equipment and the maintenance of sensitive buildings.The research on the reduction technology of vibration and noise of high-speed railway is particularly urgent.The vibration isolation barrier can effectively reduce the environmental vibration caused by railway,which can be divided into continuous and discontinuous isolation barriers.The continuous barrier displays as a whole in space,and its layout form is relatively single.The discontinuous barrier is composed of a large number of units,which is composed of a certain arrangement rule,and its layout forms are more flexible and diverse,so the value of research and development is significant.In this paper,the vibration isolation effect of single row discontinuous barrier is evaluated through the vibration isolation tests on the surface of sand foundation,and the action mechanism of barriers and vibration wave is analyzed.Under the experimental conditions in this paper,some rules and conclusions beneficial to scientific research and engineering practice are obtained.First,the isolation performance of the discontinuous barrier:(1)When Rayleigh waves with specific frequencies propagate on the surface of the foundation,the soil vibration decreases with the increase of propagation distance.High frequency vibration wave decays rapidly,medium frequency and low frequency wave are the main causes of soil vibration.(2)For isolation performance of the different types of discontinuous barrier,concrete pile is better than isolation well,PVC hollow well is similar to empty well and solid pile is better than hollow pile.(3)For hollow pile,the larger the hollow ratio,the worse the isolation performance.The isolation performance of the round pile is greater than that of the square pile and the shape of the inner cross section has little influence on the isolation effect.Hollow cavity filled with loose granular rubber,foam and other damping material is not conducive to further improve the isolation performance of the hollow pile,the study of the integrity of the damping filler should be strengthen.(4)Specifically,the isolation effect of hollow pile filled with lightweight granular foam is slightly worse than that of filling with bulk rubber;after filling the original field soil,the isolation effect of hollow pile is reduced;the filling density has no influence on the isolation performance of the backfill-soil hollow piles.Second,the isolation mechanism of the discontinuous barrier:(1)The vibration caused by the point source in the free field excites Rayleigh waves in a radial direction along the surface of the foundation.Meanwhile,the vibrations of the points along the propagation path on the surface of the foundation are gradually weakened.There is a steady transition when the ? drops to 0.6 and a placid decline when ? decreases to less than 0.25.(2)The shielding effect of pile on Rayleigh wave is as follows: the vibration shielded region is located behind the piles,and the region presents a trumpet-shaped area that takes the pile as the vertex.Increasing the quantity of piles contributes to increasing the vibration isolation effect,not only that involving the degree of isolation but also for the area of the shielded area.(3)The reinforcement effect of pile on Rayleigh wave is as follows: the vibration-strengthened regions include the diffraction regions at the pile corners on both sides of the single-row piles and the scattering region at the gaps of the piles.In addition,the composite regions are located among the vibration source and the scattering and diffraction strengthened regions.Increasing the number of piles has little influence on the scattering and diffraction strengthened regions but can significantly enhance the vibrations of the composite regions.In general,the vibration strengthened strips are connected with the scattering strengthened regions.However,in the test of a single pile,the pile is connected to the diffraction strengthened regions near its two anterior angles.