Vibration Of Track-subgrade-foundation Structure Induced By High-speed Railway And Isolation

As the rapid development of high-speed railway in China,railway speed,axle load,road network density and traffic density are gradually increasing.And the environmental vibration induced by the railway becomes more and more serious.It not only endangers the safety of surrounding buildings,but also leads to the malfunctioning of sensitive equipment and discomforts to people.Therefore,it is of theoretical significance and engineering value to analyze the vibration and study the ways about reducing the vibration.This thesis integrates theoretical analysis,laboratory tests and numerical simulation,aiming to study the propagation and attenuation of vibration wave induced by high-speed train and its influence factors about vibration isolation.The main contents and results of this thesis are as follows.(1)The dynamic triaxial tests of saturated grey muchy silty clay of layer No.4 in Shanghai area are conducted to analyze the variation of dynamic elastic modulus and damping ratio with depth by controlling the confining pressure and initial deviatoric stress.It is found that both the dynamic elastic modulus and damping ratio increase with the increase of depth,and the growth rate decreases gradually.Also,both the dynamic elastic modulus and damping ratio increase with the increase of the applied dynamic load.The logarithmic function and exponential function can be adopted to fit the relation between the depth and dynamic elastic modulus or damping ratio in a certain range.(2)The ballastless track is simplified as a double-beam model to analyze the influence of track cushion and CA mortar on the critical velocity and vibration response of track by Fourier transform.Results show that the stiffness of track cushion has a limited impact on both the critical velocity and vibration response.It is different that the critical velocity increases and the vibration response decreases with the increasing of the stiffness about CA mortar.And the existence of cushion damp or CA mortar damp can significantly increase the minimum critical velocity,but the variation of cushion damp or CA mortar damp has no effect on the critical velocity.(3)The exposition of the propagation and attenuation laws of vibration includes the types and characteristics of vibration wave,wave equations and attenuation laws in soil.And the mechanism of barrier vibration isolation is described,including the reflection and refraction of elastic wave and vibration amplification phenomenon.Finally,the evaluation criteria of environmental vibration are introduced in combination with vibration parameters and vibration evaluation indicators.All of these provide the basic principle of vibration isolation for the subsequent numerical simulation.(4)The effects of different vibration isolations and their influence factors are studied by the three-dimensional numerical models with homogeneous foundation and heterogeneous foundation.There are some results.First,the open trench has a significant weakening effect on the vibration with the frequency above 4Hz and this effect become more obvious with the increase of the buried depth about the open trench.Both the width and position of the open trench have no significant influence on its isolation effect.Then,the vibration isolation effect of the concrete filled trench is just about 2~3dB and this effect become more obvious with the increase of the buried depth about the concrete filled trench.The width and position of the concrete filled trench,and the existence of sandwich layer have no significant influence on its isolation effect.Finally,piles in row have a significant weakening effect on the vibration with the frequency above 3Hz.Effects of three influence factors are discussed in this chapter,among which the number of pile row is in the first place,the length of piles being the second and the spacing being the third.At the same time,the effects become more obvious with the increase of both the number of pile row and the length.The acceleration magnitude in homogeneous foundation is generally lower than that in heterogeneous foundation,nearly 11 dB in ground without vibration isolation.However,this difference becomes gradually unconspicuous with the increase of depth in foundation.The effective depth of the vibration isolation is about 50 m.