Study on the Piling Characteristics and Settlement Deformation of Ballasted Track Bed under Different Wet Ballast Content

Qinghui Zhu, Zhongchang Wang, Yi Yang, Wenrui Bian

Abstract In cold regions, the freeze-thaw cycle affects ballast track, causing water accumulation in the ballast bed. This results in slippery ballast surfaces, reduced particle friction, and ultimately leads to ballast bed settlement.To investigate the macro-micro mechanical behaviors of ballast with varying wet ballast contents, we first measured the aggregate angle of repose of ballast under different wet ballast conditions through laboratory tests. Subsequently, a neural network proxy model was employed to optimize the meso-contact parameters between ballast particles under different wet ballast conditions. A discrete element model of ballast bed was established to analyze the meso-mechanical behaviors of ballast particles and the overall evolution of the ballast bed under varying wet ballast contents.The results show that: (1) The smaller the wet ballast content, the greater the friction coefficient, which can effectively restrain the fluidity of ballast particles and construct a more stable ballast stacking form. ( 2) With the decrease of friction coefficient, the angle of repose of ballast decreases significantly, the displacement field response intensifies, the overall displacement amplitude increases, and the particle velocity weakens.(3) The mechanical response is most pronounced at the sleeper base and the area below the rail bearing point, where displacement and velocity decrease with increasing ballast depth. In the ballast shoulder region, particle displacement remains relatively limited, and the reduced friction coefficient causes the ballast particles 'movement to shift from vertical compaction to a distinct lateral shear flow pattern. (4) The displacement amplitude of the sleeper is inversely related to the friction coefficient, with the friction coefficient's reduction significantly increasing the sleeper's vertical displacement.