In-Track Measurements Of Crosstie-Ballast Interfacial Pressure Magnitudes And Distributions With Varying Train Operational Conditions

This paper describes the development and successful utilization of a method to measure average railroad track crosstie-ballast interfacial pressures using pressure cells specially designed for granular materials. The test method was developed and verified using a series of laboratory tests using controlled loads applied to sections of trackbed constructed in specially designed resilient frames/boxes. For the in-track tests, a number of successive crossties were fitted with recessed pressure cells at the crosstie-ballast interface below the rail seat. Trackbed pressure measurements were collected for numerous revenue freight trains during a 20-month period of traffic including numerous loaded and empty unit trains, mixed trains, and intermodal trains. Test results are also presented for complementary static and dynamic loading using the FRA DOTX 218 comprehensive test and inspection train. Measured pressures at the crosstie-ballast interface directly below the rail seat range from 20 to 30 psi (140 to 210 kPa) for typical locomotives and heavily loaded freight cars having basically smooth wheels. Wheel loads measured by nearby wheel-impact load detectors (WILDs) were compared to trackbed pressure data for the same trains traversing the test site. Measured WILD parameters were compared to recorded tie-ballast pressures. Increases in WILD loadings, due to heavier wheel loads or increased impacts, relate favorably to increases in recorded trackbed pressures. Trackbed pressures produced by revenue freight trains compare favorably with those obtained using DOTX 218 applied wheel loads.