Hybrid BPM-PRM Model for Dual-scale Degradation of Ballast

While ballast track quality evaluation is reported to depend on the fouling index, which reflects the production of fine particles from ballast particle abrasion that accumulate and contaminate the ballast track structure, ballast degradation in other modes, such as splitting and angular breakage, is also reported to govern track stability. Although the discrete element method (DEM) has advanced particle breakage modelling over decades, simulating ballast degradation, especially regarding particle shapes and the processes of fragmentation and fines accumulation, remains challenging. Currently, the bonded particle model (BPM) enables realistic particle shape modelling and particle breakage; however, it struggles to capture abrasion-generated fines, whereas the particle replacement model (PRM) can achieve this but inadequately captures ballast morphology, vice versa. To address this challenge, this study introduces an innovative hybrid framework integrating the BPM and PRM, termed the BPM-PRM ballast degradation method. Validation commences with single-particle compression tests and is followed by tn-family value analyses to independently verify the BPM and PRM components. This modelling method is validated by the initial revolutions of a Los Angeles Abrasion (LAA) test. The hybrid model successfully replicates multi-modal degradation behaviours: major breakages (e.g., splitting, angular fragmentation) and minor attrition-induced fines generation.