Insulated rail joints (IRJs) are widely used in heavy-haul lines, owing to they are safety critical components of track circuit. However, the IRJs breaks the continuity of the rail, making rail more vulnerable to damage under the long-term wheel-rail interaction. In order to study the performance of IRJs, field investigation and tests were carried out at new IRJ and damaged IRJ. At the same time, a 3D coupling model of heavy haul train-IRJ was established for the further analysis. The result shows that in regards to rail-surface regularity, the new IRJ and the damaged IRJ exhibits convex joint and concave joint respectively. IRJs will gradually turn to concave and dipped in the vicinity of end-post under long-term wheel-rail impact. Since there is a vertical rail displacement difference on both sides of the end-post between the two IRJs, causing the wheel-rail interaction has two different impact modes, of which one is downward height difference impact and the other is upward height difference impact. In normal speed, the impact caused by the damaged IRJ is larger than the new IRJ does and it leads to a severer damage to the whole track. The displacement of sleeper at the damaged IRJ is 7.6 times larger than at the new IRJ due to the void between the sleeper and the ballast. The transfer function of displacement from rail to sleeper at the new IRJ is between 0 and 0.4, while the damaged IRJ is between 0.42 and 6.1. The transfer function can be used as a vital index to evaluate the IRJ service state. With the increase of speed, the displacement of rail and sleeper at the two IRJs increases correspondingly. For the sake of decreasing the occurrence of fatigue damage and plastic deformation of rail and plate as much as possible, the maximum depth of concave should be reined within 0.55 mm.

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In order to study the interaction between various fouling particles and ballast, a multi-layer and multi-scale discrete element model (DEM) including the sleeper, ballast bed and the surface layer of subgrade was developed. Two typical fouling particles, the hard particles (sand) and soft ones (coal fines), are considered. A support stiffness test of the ballast bed under various fouling conditions was conducted to calibrate the microscopic parameters of the contact model. With the model, the influence of fouling particles on the mechanical behavior and deformation of the ballast bed was analyzed from macro and micro perspectives. The results show that the increase in the strength of the fouling particles enlarges the stiffness of the ballast bed. Hard particles increase the uniformity coefficient of the contact force bond γ of ballast by 50.4%. Fouling particles increase the average stress in the subgrade, soft particles by 2 kPa and hard particles by 1 kPa. Hard particles can reduce the elasticity, plastic deformation and energy dissipation in the track structure. As the fouling particle changes from hard to soft, the proportion of the settlement in ballast bed increases to 40.5% and surface layer of swbgrade settlement decreases to 59.5%. Thus, the influence of fouling particles should be considered carefully in railway design and maintenance.@en

High-speed railways adopt continuous welded rail to maintain the smoothness and continuity of the rail surface. However, the welded joint became one of the weakest parts. In order to clear the characteristics and mechanical properties of the new reinforced device, a dynamic three-dimensional vehicle-reinforced device-track coupling model is established. The mechanical characteristics of the track structure under high-speed train load were simulated and analyzed. After installing the new reinforced device, the dynamic response and service life of the track structure are obviously improved compared with the unreinforced rail. When the train speed is 300 km/h, the dynamic bending stress at the bottom of rail is reduced by 26.90%, the vertical and lateral acceleration of the rail are reduced by 42.78% and 21.56%, the vertical and lateral displacement of the rail are reduced by 6.36% and 8.67%, and the theoretical service life of the rail is greatly extended.

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