基于离散元−有限差分耦合的轨枕垫对有砟道床横向阻力的影响机制

The under-sleeper pad (USP) is extensively used in railway track structures due to its desired damping performance. The impact of USP on the stiffness and dynamic responses of track structures is well documented in the majority of the existing studies. However, few studies focus on its influence on the lateral resistance of ballast bed. To address this deficiency and further disclose its governing mechanisms, a refined numerical model coupling discrete element-finite difference methods (DEM-FDM) was established for the three-dimensional(3D) sleeper− USP−ballast bed−subgrade system. The numerical model was subsequently calibrated and verified by using field-measured lateral resistance results of the ballast bed of a typical heavy-haul railroad. The influencing mechanisms of USP on the multiscale performance indicators including lateral resistance of different parts (i.e., the bottom, side, and end) of the loaded rail sleeper, ballast particle motion and inter-particle contact forces were simulated and analyzed from a variety of numerical simulation scenarios. The results show that at the same level of lateral sleeper displacement, the mobilized ballast particles under the rail sleeper with USP are located in a greater depth than those under the rail sleeper without USP, thus resulting in greater lateral resistance of the rail sleeper. The unevenness of the USP surface is a major contributing factor of the increase in lateral sleeper resistance. Greater USP stiffness results in higher lateral sleeper resistance. The use of the USP can increase the lateral shear stress and the maximum normal contact forces within the ballast bed underneath the rail sleeper, both of which increase with the increase of the USP stiffness.