Numerical Simulation Of High-Speed Railway Ballast By Two-Dimensional Discrete Element Method

With the rapid development of high-speed railway, the total mileage of China has exceeded ten thousand kilometers and the operating miles ranks first in the world. However, the high speed always aggravates the wheel-rail interaction. With regard to the ballasted track, more vibration and impact are induced by the dynamic cyclic loads. Accordingly, the pace of track deterioration is accelerated and the workload of track maintenance is increased. It has been a crucial and urgent problem to guarantee the high speed ballasted track for a long-term steady operation. According to the incomplete statistics, more than90%of the ballasted track settlement is caused by the ballast bed.80%of maintenance and repair work is on the ballast bed or the track diseases induced by bed problems. Therefore, it is significant to carry out researches on the high-speed railway ballast bed.A brief overview is given with regard to the researches on ballast or gravel aggregate at home and abroad, as well as the experimental studies and numerical simulations based on the discrete element method about the ballast bed. In this paper, the two dimensional discrete element software PFC2D is adopted to simulate the ballast particles and ballast bed of high-speed railway. The research work mainly includes three aspects in this paper. Firstly, sample database of the high-speed railway superfine ballast is established in this paper. The numerical simulation experiment of ballast particles is carried out and the size effect on strength of ballast particles is examined. The Weibull distribution is used to get the37%tensile strength of different size class. In view of the randomness of the position and angle of ballast inside the track, the numerical uniaxial compression experiment of a sample ballast particle loaded from different angles is performed. The influence of loading direction on the ballast crushing strength is analyzed. Secondly, triaxial test is one of the most important methods for the ballast characters. This paper takes the biaxial test model of the high-speed railway superfine ballast to study the dynamic responses under monotonic load and cyclic harmonic load respectively. Influences of confining pressure on the strength and axial strain of the model are analyzed. The results show that increasing the confining pressure of the model within an appropriate scope is helpful to improve the strength and stability of the model. The loading rate was considered to analyze its influence on the inner particles of the model. Results indicate that under the action of impact load, particles inside the model are more likely to crush. Besides, simulations reveal that both frequency and amplitude of the cyclic harmonic loadling have influences on the axial strain of the model. Lastly, for further researches on the dynamic response of ballast bed under dynamic loads, a numerical model of the high-speed railway ballasted track is established, which is a longitudinal model with three sleepers. The cyclic harmonic load is applied to the model, and the dynamic responses of the sleeper and ballast bed under different loading amplitudes and frequencies are analyzed. Analogously, the dynamic train load calculated by the vehicle-track coupled dynamics is also exerted on the model. The corresponding dynamic responses influenced by the train speed, axle load and track irregularity are investigated respectively.This paper provides the idea and method for the micromenchanical-macroscopic mechanical behavior of high-speed railway ballast bed. The research result can be reference to forecast the track performance and maintenance.