Hydraulic conductivity estimation for ballasted railway tracks: A systematic review

Abstract

The hydraulic conductivity of railway ballast is a critical parameter governing track stability and longevity. It is severely compromised by ballast fouling, which accelerates water retention and embankment soil degradation. To address a historical decade scarcity of consolidated research, this systematic literature review synthesizes a comprehensive range of available evaluation methodologies across laboratory, field, and numerical paradigms. Following PRISMA guidelines, a systematic database search of Scopus (n = 49) and Web of Science (n = 106) yielded 155 original records. After duplicate removal, 123 records were screened, and 24 full-text reports were assessed for eligibility. Incorporating 2 additional papers from citation searching, a final dataset of 26 publications was selected for rigorous data extraction. The reviewed methodologies primarily comprise laboratory techniques (n = 19) and numerical simulations (n = 5). Synthesized findings demonstrate a substantial reduction in ballast drainage capacity with increasing fouling, a transition from non-linear to linear flow regimes
as aggregates degrade, and a significant structural dependence on fouling type and initial aggregate gradation.
Crucially, the review maps critical hydraulic parameters—specifically hydraulic conductivity, free surface dynamics, fluid flow behaviors, and permeability—across a global framework of international scientific interest, aligning findings with standards and guidelines from the USA, Australia, Europe, South Africa, Nigeria, and India. Ultimately, this study bridges a vital knowledge gap by positioning railway infrastructure as an integrated
filtering and retention facility functioning as a Nature-Based Solution (NBS). To advance the field, a numerical simulation framework is proposed to synthesize both established and emergent parameters, incorporating complex aggregate geometries and time-variant hydraulic conditions for future infrastructure design.