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Fundamental Nonlinear Track Load-Deflection Behavior for Condition Evaluation

Locations of rapid track condition deterioration are typically well known to railway track engineers, although the cause and methods of improvement may be unclear. The rapid deterioration of these locations can be due to many factors such as poor conditions of the components (rail, tie, and ballast) or failure of any of the components or subgrade. The exact cause of the problem is generally unknown as attempts to maintain the track in acceptable condition (by surfacing or undercutting) are implemented. In conjunction with track geometry measurements, which help to identify poorly performing track locations, track load-deflection behavior can contribute to the knowledge of the cause of the problem, with an ultimate goal being identification of a cost-effective, long-term solution to improving the performance of the track. Fundamentals of track load-deflection behavior, how track behavior relates to performance, indices that can be used to determine suitable maintenance strategies, and the relation of these indices to actual track performance all contribute to the evaluation. As indications of the track load-deflection behavior, several track stiffness measurement techniques that have been proposed and tested are described. The goal is to clarify the need to measure track stiffness and to identify rational means of relating the data to track condition and, ultimately, to ensure maintenance, renewal, and safety.