Theory Of Wave Propagation Of Internal Load Of Soil And Study On Vibration Of Layered Media

In order to adapt the new demand of the modern social and economic development,the scale of China's high-speed railway system is gradually expanding.During the operation of the high-speed train,vibrations are produced due to the continuous impact between the train and the track,which spreads to the surrounding area through the sleeper and the soil of the foundation.The influence scope may involve residential areas,ancient buildings,factories and laboratories using precision instruments and equipment and so on.With the increasing of the rail-system coverage in cities,the environmental vibration induced by the high-speed trains is becoming more and more prominent.Also,with the advancing of the researches about the submarine tunnel,the realization of China's submarine high-speed traffic network lines is within reach,and the same problem will occur with high-speed trains operating under the sea.To sum up,it is necessary to study the vibration problem induced by the load applied to the semi-infinite space.Using with the basic theory of the wave transmission and the finite/infinite element numerical method,the practical problem of environment vibration in the semi-infinite space induced by high-speed train can be transformed into the study of vibration response of the medium subjected to moving load.This thesis studied systematically on the problem of the load acted to the medium composed by layers with different properties,and the main contents and conclusions are as follows:(1)Based on the theory of the wave transmission in two-dimensional,the surface waves at different interfaces of the layers are derived with characteristic analysis,i.e.,Rayleigh wave at the free surface,Scholte wave at the interface between the soil and liquid,Stoneley wave at the interface of soil layers of different properties.The attenuation of the displacement amplitude along y-axis induced by the vibrations from the interfaces is analyzed and summarized,which is used to select the region of the attenuation wavenumber for the infinite elements in the 2D and 2.5D Finite/Infinite Element Method,as well as the quantification of the range of the corresponding regions.(2)The vibration problem of the single-layer soil subjected to line load applied at different positions are studied,and the the multiple factor method is proposed.The soil is divided into two parts,namely the upper part and the lower part,with wave equations in plane-type form,and the displacement and stress responses are calculated independently.When the line load changes from the free surface vibration source to an internal vibration source which applied at a certain depth of the medium,the attenuation changes from single direction for general plane waves to bidirectional directions.The actual load which produces the downward wave in the lower part is reduced by the effect of upward attenuation.The multiple factor is used to enhance the relative terms of the sress,so that the boundary conditions of load are kept while considering the bidirectional attenuation of the vibration sources in the medium.(3)The vibration problem of single-layer soil subjected to internal moving point load is studied.The 2D multiple factor method is improved with considering of the dissipation effect induced by the load moving along z-axis.Setting the Rayleigh wave velocity as the standard,the velocity of the moving load is divided into two kinds,i.e.,subcritical and supercritical.The "specific velocity",which varies with the moving load velocity,is defined as a parameter to measure the degree of dissipation,and used to adjust the multiple factor.Finally,the improved calculation method of plane-type waves is suitable for the single-layer subjected to an internal moving point load,with different velocities and self-frequencies.(4)Based on the theory of wave propagations,numerical method and 2D multiple factor,a 2D semi-analytical method is presented to analyze the vibration of layered medium.Using theoretical method,the displacement responses at the interface of layers are obtained,which is used as the fixed boundary of the finite/infinite elements.So that the full numerical model can be transformed into the semi-analytical method,only the main layer of the whole medium is needed to be modeled,and the calculation are simplified.(5)Based on the theory of wave propagations,numerical method and 2.5D multiple factor,a 2.5D semi-analytical method is presented to analyze the vibration of layered medium.The vibration response of soil with overlying liquid layer are analyzed.And only the soil are focuses on modeling,with considering of the interaction effect between liquid and soil.The innovation points of this paper are as follows:(1)The 2D multiple factor considering the double attenuation of vibration sources inside the medium is proposed,and the vibration response of the medium subjected to an internal line load is calculated by the plane-type wave.(2)The 2.5D multiple factor,which varies with the velocity and self-frequency of the moving load,is proposed,and the vibration response of the medium subjected to an internal moving point load is calculated by the plane-type wave.(3)The semi-analytical method for layered media is proposed,which can be used for 2D and 2.5D vibration analysis and greatly simplifies the computational work of the numerical model.The vibration problem of layered media is studied,and the load position,moving load velocity,self-frequency and the thickness of each layer are the key parameters in analysis.The attenuation change of vibration response is discussed in detail through the numerical examples.It is of reference value to the prediction of the influence range of vibration of the medium and the design of vibration isolation measures.