The support structure beneath railroad tracks may appear to be a simple layering of various materials, but rather, it is a complex system working together to distribute the load of passing trains. It is paramount that this structure maintain its designed support properties not only to preserve component life expectancy but to maintain the safety of the trains traveling over the rails.

During normal operations, track geometry, as evaluated through the standard deviation of various track geometry channels, tends to degrade over time. This is a byproduct of the cyclical loading applied to the track structure by passing trains causing the slow compacting and settling of the ballast and sub-structure. Assuming all variables are held constant, a regular maintenance schedule should bring track geometry back into acceptable limits, but this is generally not the case in real life. In the event that the subgrade cannot support and distribute the pressure caused from the passing train successfully, accelerated track geometry degradation can take place. This accelerated degradation can be further increased when there exists a transition between support strengths which can lead to increased dynamic loading.

A case study in sub-structure pressure management has been devised and applied to a high speed rail line. During a recent track renewal operation where track was maintained down to the subgrade, pressure transducers were placed within the sub-grade layer under both the left and right rails, inside and outside of track regions where sub-structure management has been applied. This test segment was monitored over a period of one year with both pressure and track geometry data being recorded at regular intervals.

This paper will explore the relationship between sub-structure pressure and local track geometry measurements as it relates to the monitored test segment with a region of known subgrade management transition. Numerous numerical techniques will be applied to understand the change over time of the subgrade pressure distribution capability (measured as pressure beneath the rail) and the degradation of various track geometry channels individually over time. Correlation of the pressure data to track geometry data will also be done using both raw data and data processed using numerical techniques. This will lead to an understanding of how the quality of the track support structure, specifically the track support structure’s ability to distribute pressure, can affect the magnitude and degradation rates of various track geometry channels.

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