A ballast layer is used to facilitate drainage and load transferring in railroad track structure. With tonnage accumulation, fine materials, such as coal dust, clay, locomotive sand, degraded ballast aggregate, and other small particles, will penetrate into the clean and uniformly graded ballast layer causing contamination, usually referred as fouling. Fouling is unfavorable to railroad track performance due to the reduced drainage and consequent engineering challenges including but not limited to mud pumping, excessive settlement, and reduced bearing capacity. Previous research has investigated the mechanical behavior of the fouled ballast in both the laboratory and the field environment. However, the fundamental mechanism that governs the manner in which the fouling materials are transported and accumulated in the ballast layer is not thoroughly understood. Researchers at the University of South Carolina have initiated the effort to investigate the fouling process in the ballast layer. High-fidelity computational fluid dynamics (CFD) simulation is used to study the fluid flow patterns in order to quantify the transport behavior of the fine particles within the ballast layer and potential impact to the track performance and drainage. Specifically, the ballast layer is treated as a porous material, and the fouling materials are modeled as distinct individual particles to assess the probability of their trajectory location. This paper presents the preliminary results of the simulated path of the fouling materials in the ballast layer under seepage, and demonstrates the capability of the developed algorithm to quantify the effects of the ballast layer characteristics on fouling materials transport. The findings from this study will be beneficial for optimizing shoulder ballast cleaning or undercutting practices.

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