Dynamic Characterization of Railway Ballast Mechanical Behavior during Post-Tamping Track Stabilization

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Abstract
Railway ballast maintenance commonly combines tamping with subsequent dynamic track stabilization (DTS), yet the in-motion dynamic mechanical response of ballast during these operations remains difficult to quantify. This study develops a three-dimensional discrete element method (DEM) framework to simulate a complete tamping and DTS maintenance sequence, characterize the multiscale mechanical response of ballast across spatial zones, and extract strain-dependent shear modulus and damping directly during stabilizer motion. The model is verified against angle-of-repose behavior, lateral resistance before and after tamping, and dynamic excitation responses over a wide range of loading amplitudes. Independent excitation simulations are further used to establish reference modulus-reduction and damping curves for interpreting the DTS-derived response. The results show that tamping enhances support beneath the tie but severely loosens the crib region, producing a mechanically heterogeneous post-tamping ballast state. Subsequent DTS acts as a spatially selective recovery mechanism, with the greatest improvement occurring in the zones most disturbed during tamping. During DTS, all ballast zones enter the nonlinear strain regime, with mobilized cyclic shear strains ranging from approximately to . The DTS-derived responses remain consistent with the excitation-based reference curve, indicating strain-dependent stiffness degradation comparable to that observed under controlled excitation. Stiffness degradation and damping mobilization are strongly zone dependent and governed by local confinement and contact-network evolution. The proposed framework provides a particle-scale computational basis for evaluating ballast disturbance during tamping, interpreting in-motion stiffness degradation and damping mobilization during DTS, and supporting future stabilization parameter optimization.

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