Quantitative Methods Of Morphological Characteristics And Its Application Of High-Speed Railway Ballast

The granular ballast bed has become the weak link in the bed structure in high-speed railway ballasted track, with a serious impact on the running safety, comfort and the track maintenance cost under long-term service. Therefore, the research on the series of problems in granular ballasted track with high-speed and large capacity under long-term service is imminent accompanied by the development of high-speed and heavy freight for modern rail network system becoming a major national transport strategy. However, the elastic-plastic model based on the continuous medium is difficult to accurately describe the graded gravel micro-structure and mechanical support skeleton, characteristics of granular mixtures and mechanical nonlinear, and can not be used to analyse and study the effect on aggregate macro-mechanical properties caused by the morphological characteristics of different grain level ballast in the range of particle size distribution (Gradation). The graded gravel ballast particle size distribution and morphological characteristics have an important effect on the aggregate mechanical properties. Obviously, the introduction of DEM for the complex morphological characteristics and the characteristics of granular mixtures of railway graded crushed stone is strictly and relatively reasonable. With the application of DEM program, the one hand, it is very useful to carry out the study of the meso contact mechanical behavior between ballast gravels and the research on the evolution and deterioration behavior of the aggregate mechanical properties under long-term service; On the other hand, some laboratory and field tests which can not be implemented due to funding, time, technology and other factors, could be completed by numerical simulation to improve test efficiency as a good tool.The main work done in this paper is listed as follows:1. This paper focuses on the high-speed railway ballast in Track Transportation Laboratory of Southwest Jiaotong University. The research on the description methods of ballast gravel morphological characteristics and the quantitative method of graded ballast aggregate with the grade generation program has been carried out after the preparation of a simple railway ballast database. Then the gravels boundary geometry parameters were extracted including surface texture, meso-scale angularity (roundness) and macro shape features based on DIP. The results show that the Fourier analysis method is capable to reflect the morphological characteristics of the ballast gravel well, and a method to quantify morphological characteristics including surface texture, meso-scale angularity (roundness) and macro shape features in the grading of high-speed railway ballast aggregate is provided.2. A method of particles graded sieving based on digital image processing (DIP) depended on the graded sieving size threshold (Xh parameter) with the correction formula is provided and the method to calculate the ballast flaky and elongated threshold is described with the application of the morphological characteristics analysis method. There are theoretical foundations for the realization of Graded Gravels Screening System based on DIP.3. The high-speed railway ballast DEM modelling methods were conducted based on the software program PFC2D with the application of DIP. Then the Hexagonal cell ball method was used for ballast particle modelling in this paper. Soon afterwards, PFC2D biaxial numerical experiments based on DEM were constructed with the preparation of gradation generation program to carry out the research that the effects on the process of shear failure and the response of axial stress vs axial strain in different micro-parameter range and different sizes of the cell ball of ballast particle, and the model has been verified. The study has been given the relatively reasonable micro-parameters for the numerical simulation of the real shape ballast particles aggregate.4. The aggregate numerical simulation analysis in different Fourier index quantitative indicators based on Fourier morphological characteristics quanti-tative methods and the ballast particle with the PFC2D Hexagonal cell ball modeling method in the aggregate graded with the preparation of gradation generation program have been carried out. Then another analysis of numerical simulation that the bond can be broken in ballast particles have been carried out afterwards, which clarify that the PFC2D modeling method and the graded aggregate Fourier morphological characteristics quantitative methods have good application prospects in the granular ballast bed engineering.