Discrete element analysis of the influence of sleeper longitudinal creeping on the degradation of ballast bed lateral resistance

Abstract

With the continuous expansion of mountainous railway networks, the stability challenges posed by longitudinal sleeper creeping in steep-gradient sections of continuous welded rail systems have become increasingly prominent. This study addresses the lateral resistance degradation of ballast beds induced by gradient-directional sleeper creeping. A refined three-dimensional sleeper-ballast bed coupling model was developed using the discrete element method, enabling coupled simulations of multi-stage longitudinal displacement loading and lateral resistance testing. The investigation systematically elucidates cross-scale mechanisms governing lateral resistance characteristics, mesoscopic contact redistribution, and ballast migration patterns under creeping conditions. Key findings reveal that longitudinal displacements reduce lateral resistance by 2.40 kN during the initial loading phase (0–1.0 mm lateral displacement) through weakened sleeper-base constraints and intensified leading-side friction. The resistance evolution exhibits triphasic behavior: differentiated growth phase (2.40 kN inter-case disparity), differential attenuation phase (disparity reduced to 1.22 kN), and stabilized equilibrium phase (0.66 kN residual difference). Longitudinal creeping fundamentally redistributes lateral resistance components, decreasing the sleeper-base contribution from 57 % (0 mm creeping) to 22 % (5 mm creeping) while increasing leading-side participation from 14 % to 53 % via enhanced ballast compaction. The asymmetric disturbance pattern amplifies particle migration in leading-side crib zones during lateral loading, creating pronounced spatial heterogeneity detrimental to ballast bed uniformity and stability. These findings establish a theoretical framework for optimizing CWR anti-buckling designs and implementing scientific maintenance strategies in steep-gradient railway sections.