Track Mechanics

Track maintenance effects the stability of track mainly by changing the ballast structure and tie-ballast friction available to resist track buckling loads.  The structure of heavily interlocked ballast is broken down during surfacing as the track position is aligned to correct track settlement and track geometry deviations.  The rail neutral temperature is also impacted by maintenance.  Combined, both the change in rail neutral temperature and the lateral resistance changes can impact track safety making it critical to reestablish track lateral resistance by compacting and consolidating ballast.  In this study, the track lateral resistance before and after surfacing was measured.  Then, various track stabilization methods were compared including dynamic track stabilizer and application of traffic.  

Sites with large vertical deflection due to loss of track vertical support were assessed to document track and site conditions as well as effects on the track superstructure.  In the photo below, the track vehicle is loading the track and the effect of the track transition is clearly visible in the image which reflects the deflection variation across the change in stiffness.  The lifted spikes are one sign of the stiffness change effects on the track superstructure. 

In older or deteriorated track segments, the gage rod can be seen as a tool to maintain proper track gage and prevent wheel drop due to gage widening.  As wooden ties age, gage widening risk increases due to tie deterioration, breakage, or rot in the rail seat area as well as spike/plate deterioration.  In concrete ties, elastic fasteners often overcome many of these failures, but missing spikes and insulators as well as pad wear can result in distinct behaviors that increase gage widening risk.  The development of deployable gage restraint measurement system (GRMS) axles and high rail truck deployment resulted in a reconsideration of several parameters.

In concrete tie track, wear of the rail seat presents some unique challenges that resulted in gage widening from a mode previously thought to present less of a risk: rail rotation.  While elastic fasteners generally prevent rail translation, deterioration in elastic fasteners can result in distinct behaviors that increase gage widening risk due to rail rotation.  The development and testing of deployable gage restraint measurement system (GRMS) axles at higher lateral to vertical (L/V) combinations was shown to highlight areas of rail roll risk.