The sand intrusion in railway tracks in sandy regions can significantly change the mechanical behaviour of tracks and thus threaten the safety of train operation. This paper presents substantial field tests on both sandy and clean railway tracks to study the effect of sand intrusion on the longitudinal resistance of ballast bed and the vibration behaviour of track structures. After that, a 3D multi-scale the discrete element model is developed to study the micro-contact between ballast particles and the vibration behaviour of sandy tracks during train passing in detail. Also, the effect of train speeds and axle loads on the mechanical behaviour of sandy tracks is discussed. The results show that the sand intrusion increases the vibration acceleration amplitude of rail and sleeper by 11.3% and 50.3%, while ballast bed decreases by 44.9%. Besides, the sand intrusion significantly changes the energy distribution in the track, wherein the frequencies of the highest energy of rail and sleeper are increased while that of the ballast bed is decreased. The parametric study shows the high train speed can cause the increase in overall acceleration of the ballast bed and high axle load can cause an increase in the micro-contact forces between ballast particles, diffusion angle of the contact force chain, displacements of ballast particles, acceleration of ballast particles, and sleeper displacements.

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Turnout is the key component of the railway tracks for trains to change direction, which is vital to operational safety and passenger comfort. Therefore, it is of great importance to perform a scientific and reasonable tamping operation for turnout areas. In this paper, based on the commercial software EDEM and RECURDYN, a coupled simulation model of the large machine tamping device-rail-sleeper-ballast bed in the turnout area is jointly established, and the correctness of the model is verified by the test results of the lateral resistance of the ballast bed. The influence of tamping operation on the macro-and micromechanical properties of ballast bed at the switching part of railway turnout areas is studied and recommendations for the optimization of tamping operation are proposed. The results show that in the squeezing stage, strong force chains are distributed concentrately under sleepers, where the distribution range is approximately elliptical with a depth of 150 mm. After tamping, only the 200-mm ballast under the sleepers is compacted, where the compactness is increased by 5.9%. On the contrary, the compactness of the ballast in the sleeper crib is reduced by 27.4%, which is the weakest part. To ensure favorable tamping quality, the tamping sequence at the switching part of railway turnout areas is suggested to be conducted in order of first through track and then diverging track.

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Due to the limitation of the geological environment, many railways around the world are built in desert areas. The intrusion of sand particles can increase the stiffness of ballast beds and cause corrosion and fracture of fasteners, turnout blockage, etc., even affecting the service safety of railways. In the paper, based on the results of field and laboratory tests, a three-dimensional discrete element model of the sandy ballast bed is developed to study the effect of sand intrusion on the load sharing ratio of sleepers, contact forces between ballast particles, displacements of ballast particles, and energy dissipation in ballast beds. The results show that the axle load in sandy tracks is mainly shared by three sleepers under the single-axle load and six sleepers under the dual-axle load. The maximum contact force under the sleeper in the sandy ballast bed is about 80% larger than that in the clean ballast bed and its normal and tangential contact forces are also larger than that in the clean ballast bed. The ballast particles at the ballast shoulder of the clean ballast bed move downward in the direction of less than 45°, while those in the sandy ballast bed move outward at the direction of 90°. The sand intrusion inhibits the movement of ballast particles and may cause a rheological phenomenon of ballast particles at the ballast shoulder. The intrusion of sand particles mainly affects the elastic strain energy and damping energy in ballast beds but has less effect on friction energy and kinetic energy.@en