An Analysis Of Dynamic Response Of Subgrade To High-speed Moving Traffic Loads With Three Degrees Of Freedom

High-speed train has been widely applied in the world due to its efficient, economic, environmental and other operational advantages. Also, the problems of the wave spreading in orbit and ground have attracted wide attention as the high-speed trains are put into operation in various countries. Because the high-speed train load will have a great impact on the vibration of the foundation with the increase of the train speed, the study of the vibration mechanism and the induced ground vibration has become one of the hottopics on the recent research.Based on the investigation of traffic condition and the vibration problems appeared in city development, the necessity of the research on train-induced environmental vibrations was emphasized. The main research contents and the means used in the field of train-induced free-field and building vibrations were summarized, and a systematic literature review was presented. The domestic and foreign research state and basic concepts of the vehicle dynamics, track projects and subgrade engineering were reviewed in detail respectively.Considering the characteristics of the whole system composed of high-speed railway vehicle system-Ballasted/ballastless track-the foundation, this thesis took three degrees of freedom system as the train load model with the consideration of the bogies and a dynamic analysis model for the vehicle with two suspensions system-Ballasted Track/Ballastless Track-Vertical Ground was developed. Then based on the basic elastic dynamic equations, using Fourier integral transform, we can derive the expressions of the vertical displacement of soil surface and the acceleration in space coordinates under the train loads when it is exerted on Ballasted Track-half space and Ballastless Track-half-space.A computational program for analyzing the dynamic responses of train-induced foundation vibrations was developed by using Mathematica 7.0, which is based on the theories presented in this thesis. The train-induced free-field responses were calculated and the ground vibration characteristics and the influence of many factors on the vibration were analyzed systematicly through some examples. Effects of different train body and different orbit on ground motions were discussed. At the same time, the influence of the propagation distance and train speed on the soil surface vibration were also analyzed. Because the surface vibration is an important factor in measuring the dynamic impact on the buildings nearby the train induced by traffic load, the analysis model and the theory presented in this thesis will play an important role in the prediction of train-induced environmental vibrations theoretically and practically. The conclusions obtained in this study can also be very useful in the optimum design of ballast-less slab track and can also provide the working basis for the further research.