Simulation Of Ballast Deformation Characteristics Utilizing DDA

ABSTRACT:The ballasted track has a history of 180 years. Although ballastless track technology has developed rapidly in recent years, ballasted track is still the most common and widely used form. The advantages of ballast track structure include simple structure, inexpensive cost, convenient maintenance. The deformation and differential settlement of ballast have a great effect on the safety and comfort, even on the railway maintenance costs, all of these make it to be an important reseach topic.In this paper, discontinuous deformation analysis(DDA) theory is used to simulate the mechanical properties of ballast. The ballast model is simulated by a randomly generated convex pentagon particles, and the real ballast gradation is got by controlling the ballast size and number. First calibrate the model parameters by inversion, then study the effect of gradation on the density and the response to the ballast uniaxial, triaxial deformation.The simulation results of ballast under the uniaxial compression and cyclic loading show that:the void ratio of ballast has the greatest impact on the deformation characteristics, the uncompacted ballast will be manifested in the elastic stage and elastic-plastic stage; although the compacted ballast will remain the elastic properties basically, the residual strain after unloading is small. After repeated cyclic loading, the residual plastic strain will decrease progressively.The simulation results of ballast under triaxial compression and shear simulation show that:In the triaxial isotropic compression, the axial stress increased with increasing strain, but the value is about half of the uniaxial compression. Triaxial shear process can be divided into two phases, the contraction is mainly due to pore compaction, following the trend of contraction decreases, especially under low confining pressure, the dilatancy will take place. As confining pressure increases,this effect is getting unclear until disappear.The ballast gradation analysis shows that:the void ratio of single size is relatively high, adding small size particle to the large particle can reduce the void ratio and increase density. For a mixture of two particle size, there is an optimal ratio, making the ballast to achieve the minimum void ratio.