Research On Model Test System Of High Speed Railway Subgrade And Dynamics Analysis

Higher requirements were needed to the design of subgrade of the railway while the speed of the train continuously increased. Fully understanding the dynamic response of the subgrade was the need for the design of high speed railway subgrade and ensuring safety and high efficiency of the railway transportation. Large scale model test has been the important analysis method to research the dynamic characteristics of the high speed railway subgrade. In this paper, aiming at the disadvantages of the recent model tests,1:1track-subgrade dynamic model test system has been established and how each factor effect the dynamic response of the subgrade under the action of high-speed train has been analysed. The main research results are as follows:1. Aiming at big difference between the small scale model test and in-situ monitering,1:1track-subgrade dynamic model test system was established, which was consist of3parts, counter-force and dynamic loading system, data testing and colletion system and high speed railway subgrade model. The system can be used for simulating how each factor affect the dynamic response and accumulated deformation of the subgrade, such as the type the train, velocity of the train, the type of the track, environment factor and so on.2. Aiming at difficulty in find proper filling in site, experiment research was carried out to determine the improvement plan of unfitted subgrade filling. Test results show that:(1)with the increase of percentage of the coarse particles, maximum dry density firstly increased and then decreased, and the optimum moisture content linearly decreased;(2) in the process of triaxial shear test, high gravel content filling trend to dilate while shearing under the low confining pressure, low gravel content filling trended to shrank while shearing under the high confining pressure;(3) for the same gravel content filling, the internal friction Angle trended to decrease as the confining pressure increase, and under the some confining pressure the internal friction angle trended to increase as the gravel content increase. However, when the gravel content is larger than60%, the rate of the internal friction angle significantly decreased and even no increase. Based on the comprehensive analysis of the results of tests, gravel content is determined by60%. And this improvement filling was adopted to construct the subgrade in the model test. The detected results after model test construction proved that the improved filling met the high speed railway subgrade filling requirements.3. Aiming at the phenomenon that the current model test only use single wheel or single axis to apply loading ignoring the stress superimposition, dynamic loading device was designed for the high speed railway model test. The design was based on essence phenomenon that the fastening conduct the force in the ballastless track of high speed railway, several actuators was set to simulate the train loading. The dynamic loading simulation devices not only could provide dynamic load of different axle load at different speed, but also could consider the superimposition effect of different wheels of adjacent bogie of adjacent car.4. Finite element analysis software was adopted to analyze that how each factor effect the dynamic response of the subgrade under the action of high-speed train. Analysis showed that:(1) vertical dynamic stress and vertical dynamic displacement in the subgrade exponentially attenuated with depth. Through the upper layer of the subgrade, dynamic stress and dynamic displacement respectively attenuated about40%,60%, and only10%left when reaching the bottom of the subgrade;(2) vertical dynamic stress and vertical dynamic displacement amplitude linearly increased as train axle load and train speed increased in the upper and bottom layer of the subgrade. However it was seemed that the bottom of the subgrade (3m deep in subgrade) was unaffected;(3) adopting0.2-0.4m for thickness of concrete bearing layer can meet the design requirements, definitely the thicker is safer, low strength concrete can be used for bearing layer to save the cost. The thickness of the bottom layer of the subgrade should be taken more than2m.