Effect of fastener failure on the micromechanical properties of railway ballast bed

Fastener failure is a critical issue affecting the performance of ballast tracks, significantly influencing the behavior of the ballast bed. This study investigates the micromechanical properties of ballast beds under fastener failure conditions using a Discrete Element Method (DEM) simulation model that accurately represents the real shape of ballast particles. The model's validity is confirmed by comparing simulation results with field measurements. Through this model, the study analyzes the effects of train load and fastener failure on ballast particle vibration, contact force, rotation, and relative sliding. Particular attention is given to the impact of the number and longitudinal distribution patterns of fastener failures. Results show fastener failure reduces vibration, angular velocity, and relative sliding of ballast particles within the corresponding ballast box and decreases the number of strong force chains. It increases the vibration, contact force, and angular velocity of ballast particles in adjacent ballast boxes on both sides, accelerating ballast bed settlement and ballast particle crushing and powdering. Notably, the impact of two adjacent fastener failures is more pronounced than that of a single failure, and consecutive fastener failures have a greater effect than alternating ones. Furthermore, fastener failure enhances particle relative sliding between adjacent ballast boxes, compromising the geometric stability of the ballast bed. These findings provide new insights into how fastener failure patterns influence the service performance of ballast tracks.