Numerical investigation of sleeper geometry effects on ballast longitudinal resistance using a coupled DEM-MBD approach

Longitudinal resistance is critical for ballasted track stability. An innovative X-shaped sleeper was developed to enhance this performance. A coupled DEM-MBD model of a full-scale ballast-sleeper-subgrade system was established to investigate the effect of sleeper geometry on longitudinal resistance and mechanisms. Results show a single X-shaped sleeper increases longitudinal resistance by approximately 27.2% over double I-shaped sleepers. Both types exhibit comparable end and bottom resistance, but the X-shaped sleeper’s V-shaped arms significantly improve ballast interlocking, nearly doubling side frictional resistance. Microscopic analysis indicates the X-shaped sleeper mobilizes a broader range of particles, engaging more ballast in resisting movement. Stress analysis reveals stress under I-shaped sleepers concentrates beneath the crib, whereas the X-shaped sleeper transfers stress into shoulder ballast and deeper subgrade, enabling subballast and subgrade layers to enhance trackbed stability through compaction and disturbance. These findings support the application and optimization of X-shaped sleepers in ballasted tracks.