Analysis of the effect of shoulder cleaning on particle migration within ballast based on a coupled CFD-DEM approach

The ballasted track is vulnerable to fouling caused by penetration of foreign materials or degradation of ag-gregates. Proper maintenance can open the clogged drainage path within the ballast and ease other track issues for both short-time and long-term use. Shoulder cleaning is one of the popular ballast manntenance methods that present promising results in the field practices. Therefore, insights of flow physics coupled with particle dynamics within the fouled ballast will benefit maintenance decision makings. This paper presents a simulation-based analysis on the effect of shoulder cleaning on fine particle migration and its influence on ballast drainage. Various factors governing particle-laden gravity-driven flow within the ballast with and without shoulder cleaning are considered, including the fouling index, fouling profile, and cohesive energy density (interparticle bonding forces that depend on the contact area between two particles). The simulations for fine particle migration are carried out under multiple different fouling scenarios using the computational fluid dynamics and discrete element method (CFD-DEM) to capture the interactions between fine particles/particles and fine par-ticles/flow. A parameter named 'local fouling index' is introduced for the first time to track the particle migration at different regions within the ballast, characterize the local fouling conditions, and evaluate the non-uniformity in fouling severity. The results indicate that the particle migration behavior is considerably influenced by those factors above, and shoulder cleaning is more effective for particle removal and drainage restoration when the fine particles trapped in the ballast have higher cohesive energy densities.