Predicted and Measured Resilient Response of Track

Field measurements were made at the Facility for Accelerated Service Testing (FAST) research track in Pueblo, Colorado to determine the magnitude of resilient or elastic stresses, strains and deflections in the ballast, subballast and subgrade resulting from train loading. These data were analyzed statistically to determine significant trends. A computer model, GEOTRACK, was used to predict the results measured at FAST for comparison with the experimental data. Then the influence of variations in the parameters on track response was demonstrated with GEOTRACK calculations. In general, the strains and deflections did not differ significantly with changes in ballast thickness and ballast type and tie type, compared to the variations within one test section. However, the ballast strains were much larger in the wood tie sections than in the concrete tie sections, apparently because of tie spring-up. The subgrade stress in the concrete tie section was larger than in the wood tie section. This appears to be a result of more uniform pressure distribution beneath the wood ties in the field, because the GEOTRACK model did not indicate such differences for homogeneous ballast layers. The GEOTRACK model showed that the most important parameters influencing track response were ballast depth, tie spacing and tie stiffness.