Case Studies

Case studies illustrate the types of challenges we routinely handle.

Measurement of track deflection and assessment of track stiffness effects on track performance provide unique insight to track load distribution and track geometric stability.  The most common issues develop with soft track support and low track stiffness.

This case study highlights the effect of very high track stiffness, low track deflection on track geometry and track structural performance.  The high stiffness limited the ability of the track to distribute loads appropriately, concentrating load on the tie below the railroad wheel.  The reduce load distribution caused high tie-ballast contact stress leading to tie bottom abrasion. 

A forensic analysis could not identify a single factor leading to reduced service life of some generations of specific concrete ties.   A review of the locations where tie performance problems developed highlighted the potential for track settlement and the formation of ballast gaps.  A review of the impact of the tie-ballast gap on tie performance was conducted including a structural dynamic assessment of changes in tie dynamic response.  The analysis included bending and vibration mode frequency shifts that highlighted a vibration mode shift when the tie changed from supported by ballast to hanging above the ballast.   

A site investigation and measurement campaign to assess the relative contribution of damage from freight and passenger traffic was undertaken.  The specific test sites served as alignment areas where data from systemwide measurement of track geometry, track deflection, and ground penetrating radar were used to assess zones of similar track performance.  For each zone, the relative degradation was used to assess maintenance tamping intervals to develop a basis for assessing expected increases in maintenance with increased freight axle loads.