Impact of Incremental Loading on Instrumentation Response in a Full-Scale Railroad Test Section Trafficked with a Heavy-Vehicle Simulator

Rail is a key infrastructure component for military asset movement, and the design and evaluation of these rail structures is important to ensure adequate support for military loading conditions. The current military design methodologies are outlined in U.S. Department of Defense Unified Facilities Criteria (UFC) 4-860-1 Railroad Design and Evaluation ; however, there is a need to advance current practices toward a more robust mechanistic-empirical design methodology. To support this effort, a full-scale test section was constructed to collect controlled instrumentation response data at applied loads ranging from 10 to 100 kips, primarily to assess the impact of a relatively stiff subgrade (10 California bearing ratio [CBR]) and a relatively weak subgrade (2 CBR) on track structural response. Instrumentation included earth pressure cells at various locations in the track structure, deflectometers in the subgrade, and strain gauges on the rail. The response data were analyzed and comparisons were made between the measured response values and the calculated response values from the existing military design methodologies. It was found that the subgrade support had a meaningful impact on measured stress, and that the measured stress was approximately 30% higher in the 10 CBR test item than in the 2 CBR test item. Deflection data indicated that plastic deformation occurred in the weak subgrade but did not occur in the stiff subgrade. The comparison to the design procedures indicated that the design stresses were lower than those measured from the instrumentation response. These data suggest that the current design methodologies could result in an under-designed rail structure.