Mitigation of differential movements at railroad bridge transition zones

Railroad transitions are track locations that experience a rapid change in track structure, such as a bridge or crossing. These locations are prone to differential movement and require frequent resurfacing to maintain an acceptable track geometry for both passing freight and high-speed passenger trains. In an effort to reduce the frequency of track resurfacing, an instrumentation and numerical modeling study was undertaken to (1) identify the root causes of the differential movement at transition zones, (2) develop and improve existing measurement techniques to evaluate track performance, and (3) recommend potential design, remedial, and resurfacing techniques to reduce and/or mitigate the differential movement. The two objectives of the field instrumentation program are: (a) develop a general overview of the loading environment and track movement and (b) develop a mobile system that focuses on tie behavior by measuring rail and crosstie displacements. Three-dimensional dynamic numerical modeling of bridge transition zones was also performed to investigate how changes in ballast settlement affect the transition zone loading environment. Based on field measurements and numerical modeling, three “root causes” were identified for differential movement at railway bridge transitions: (1) lack of track displacement on the bridge to balance transition zone track displacement, (2) increased applied loads in the transition zone, and (3) reduced-performance ballast conditions in the transition zone. To prevent the observed permanent vertical displacements, the following recommendations for future transition design are: (1) increase transient and permanent track displacements on the bridge to balance approach settlements, (2) use compacted and durable ballast and a working drainage system in the approach, (3) reduce ballast and subgrade settlement by increasing approach confinement in the approach, and (4) installing a resilient layer between the bottom of the concrete tie and top of the ballast to reduce ballast and tie degradation