Experimental study and discrete element analysis of ballast bed with various sand content

Abstract

The railway in the desert region has to face sand hazards. It is of great significance to study the influence of sand on the service quality of railway, to understand the effect of sand on the mechanical characteristics of track structure, and to provide a guide for the maintenance work. At present, the laboratory tests and finite element simulation models are mainly used for the research on sandy railways, while there are few field tests and theoretical analysis methods. In this paper, a discrete element model considering sand, sleepers, ballast bed, and surface layer of subgrade is developed for this purpose. The sand is generated using a new method named the Adjacent grid filling method. The model has an advantage in modelling the mesoscopic contact characteristics between (irregular shape) sand particles and ballast particles. The model is validated against the laboratory test of sand repose angle and the field test of sleeper displacement have conducted. Using the model, the influence of sand content on the mesoscopic contact characteristics and energy evolution of the ballast bed is analyzed. The results show that irregular sand particles with various roundness can better simulate the occlusive effect between sand particles. The higher the sand content, the stronger anisotropy can be seen in the contact number distribution and the influence of sand content is more significant on the tangential contact number distribution than that on the normal contract number distribution. With the increase of sand content, the vertical stress and transverse stress of ballast bed increase at first and then decrease slowly, wherein the 30% sand content is the critical point for the change. The kinetic energy, contact friction energy, and contact damping energy of particles in the ballast bed decrease and then increase slowly with the increase of sand content, while the elastic strain energy in the ballast bed decreases gradually. The results show that when the sand content in the ballast bed is 30% or above, the maintenance is recommended to be conducted a timely manner.