Comparative analysis on movement and vibration energy characteristics of ballast particles in heavy-haul railway transition zone

The dynamic responses of ballasted trackbed under repeated action of heavy⁃haul train loading are closely related to the supporting stiffness of underlying structures and meso⁃scale movement characteristics of ballast particles; however, no quantitative influence laws and correlation mechanisms have been reported yet. To address this knowledge gap, a field test study was conducted at one typical embankment⁃bridge transition zone of the flagship heavy⁃haul railway corridor dedicated for the coal transportation. The innovative wireless particulate sensors(SmartRocks) were embedded at different locations within the ballasted trackbed to monitor real⁃time motion of ballast particles during the passages of heavy⁃haul trains. The field⁃recorded data were then analyzed to compare variations of ballast particle movement and vibration energy with different levels of supporting stiffness of underlying structures both along longitudinal track direction and within track cross⁃sections. The research results show that the vertical acceleration and rotation angle responses of ballast particles underneath crossties caused by repeated moving train loading are clearly periodic, and the rotation angles in the horizontal plane are relatively large and irreversible. The two adjacent bogies of two neighboring railcars can be treated as a loading unit to study the vibration characteristics of ballast particles. The vertical motion of ballast particles dominates in the embankment⁃bridge transition zone and at the bridge platform and bridge mid⁃span, followed decreasingly the by longitudinal motion. The vibration energy levels of ballast particles underneath the rail⁃supporting areas located at the bridge mid⁃span are about 2 to 3 times those above the embankment. The inter⁃particle contact forces of ballasts increase with the supporting stiffness of ballasted trackbed increases, and the upward acceleration values increases gradually until approaching the downward acceleration values. The vibration amplitudes of ballast particles above the stiff support are relatively great with periodic features, which may be attributable to the relatively pronounced superposed vibrations of stiff structures overlain by ballasted trackbed. Ballast particles underneath the ends of crossties located in the severely fouled and hardened zones above bridge deck barely rotate, thus special attention should be paid during the routine maintenance operations. The research results could provide theoretical basis and technical guidance for intelligent health monitoring, accurate dynamic performance recognition, and active degradation risk warning of heavy⁃ haul ballasted tracks. © 2023 Editorial Office of China Civil Engineering Journal. All rights reserved.