| With the rapid development of the national economy, the construction of China Railway of High-speed has been comprehensively launched. During the period of the eleventh five-year plan, by constructing high-speed passenger dedicated railway, developing intercity passenger railway and upgrading the existing line, China will preliminarily form the express traveler network connecting the large and medium cities, of which the mainstay is high-speed passenger dedicated railway. The passenger dedicated railway is constructed with a speed of 200-350km/h, which makes the dynamic load intensity that the rail-subgrade system bearing increase and the vibration of the rail-subgrad system under the train load aggravate. And ballastless track is used widely, which leads to a high requirement to de subgrade. So the design of the high-speed railway must carry out a dynamic analysis, which includes calculations of the deformation of the rail-subgrade system, the dynamic stress, acceleration in the subgrade and their distribution under the train load.The paper first summarizes the research status of the dynamic response of the high-speed railway subgrade home and abroad. In China, the ballastless track is just beginning. The study of the ballastless track-subgrade is weak, which is focus on the couple analysis of the train-track system, while the research on the subgrade to matching the ballastless track is relatively less. And lots of existing studies on effects of the dynamic response caused by subgrade parameters are relying on two-dimensional models. As the ballastless track-subgrade system is a spatial structure, using the plane model will lead to error, especially in low frequency region, plane model will significantly underestimate the dynamic response of the real spatial structure. The rail ditch and fastener also made the rail-subgrade an inhomogeneous structure longitudinally. So using the three-dimensional model to study the dynamic response of the rail-subgrade system and effects of the dynamic response such as dynamic stress and acceleration as well as their distribution caused by subgrade parameters is urgent to be strengthened.Secondly, the paper analyzed the elastic-plastic mechanical properties of the rock and soil, and generalizing its elastic-plastic constitutive relation. The paper also summarized the finite element method of the elastic-plastic problems and dynamic analysis.Thirdly, according to the typical section of the ballastless track-subgrade, the paper established a finite element model of slab ballastless track-subgrade multi-layer system by using the finite element software ANSYS. Then it determined the calculation parameters. It analyzed the contact of the rail and the rail ditch, and also improved the derivation of the constraint equation which is about the contact of the beam element and the spring-damper element. And this paper analyzed the selection of the reasonable high-speed train load.The main work of this paper was doing the transient dynamic analysis of the rail-subgrade three-dimensional finite element model by using ANSYS. Then it extracted the vertical dynamic deformation and vertical acceleration of the rail, the vertical dynamic deformation, the maximum compressive stress, the maximum tensile stress and the maximum shear stress on the surface of the subgrade, as well as the acceleration and the equivalent stress of the subgrade. The it analyzed the dynamic response which included the transverse distribution of the response on the surface of the subgrade, the time history curve of the response of the rail and on the surface of subgrade, as well as the attenuation of the acceleration and equivalent stress in the subgrade. By changing design parameters such as velocity and the elastic modulus of every layer of the subgrade, it discussed the influence law on the distribution of the response and performance of the rail-subgrade system which is caused by these parameters. The paper comes to the following conclusions which can provide evidence for the optimization of the subgrade structure.(1) the law of related dynamic response changing with the time, its transverse distribution and attenuation with depth:The superposition load of each carriage acting on the subgrade does not affect the peak of the dynamic response, so while it is carrying out simulation, considering one bogie or several bogies does not influence the result of the dynamic response of the rail-subgrade system great. The maximum of the dynamic stress of the subgrade bed surface is under the edge of the concrete bearing plate. With the depth increasing, dynamic responses diffuse and attenuate. The vertical acceleration and the dynamic stress decrease as the depth increases. The vibration of the foundation is much weaker than the vibration of the subgrade, and the equivalent stress in the foundation has already been in a low lever. As for the chosen calculating model, the vertical acceleration has attenuated 94.1% in the subgrad, and the equivalent stress has attenuated 87.9% in the subgrad.(2) the influence law of related dynamic response caused by elastic modulus of every layer of the subgrade and the foundation:①With the elastic modulus of the surface layer increasing, the vertical dynamic deformation of the subgrade surface decreases, while the maximum principle stress and the maximum shear stress of the subgrade surface all increase. All those related dynamic responses change more and more slowly as the elastic modulus changes. The acceleration in the surface layer of the subgrade bed becomes slow as the elastic modulus of the surface layer of the subgrade bed increase.②With the elastic modulus of the bottom layer increasing, the vertical dynamic deformation of the rail, the vertical dynamic deformation, the maximum principle stress and the maximum shear stess of the subgrade surface all increase. All those related dynamic responses change more and more slowly as the elastic modulus changes. The attenuation of the equivalent stress in the subgrade bed becomes slow as the elastic modulus of the bottom layer of the subgrade bed increase.③The changing of the elastic modulus of the subgrade fill affects the related dynamic responses less, except the equivalent stress in the subgrade.④The vertical dynamic deformation of the subgrade surface decreases as the elastic modulus of foundation increases, and it changes more and more slowly as the elastic modulus changes, while the vertical acceleration of the rail and the subgrade increases.⑤When the elastic modulus of the certain layer of the subgrade changes, the equivalent stress in the changing layer will increase as the elastic modulus increase, and it will affect a certain zone beneath the changing layer. When the changing layer is not the surface layer of the subgrade bed, it will also affect a certain zone beneath the surface of the subgrade, in which the equivalent stress will decrease as each elastic modulus increase.(3) The paper got the influence law of related dynamic response caused by different velocity.
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