It has been desirable for years to develop a reasonably simple, direct, accurate, and reliable method to measure pressure distributions in railroad trackbeds, especially the pressure magnitudes and distributions at the tie-ballast interface. In this study, specially-designed granular material pressure cells were used to measure pressure magnitudes and distributions. The cells were placed directly under the rail-tie intersection at the tie-ballast interface.
Initially, a MTS test machine was used to conduct a series of laboratory tie-ballast box tests for a wide variation of ballast types and loading configurations. The adequacy of the cells for in-track measurements was verified with a series of very controlled laboratory tests and measurements using simulated trackbed sections and loading conditions. Excellent correlations were obtained comparing applied machine pressures and measured transferred cell pressures indicating that this type of pressure cell is suitable for in-track tie-ballast pressure measurements. This preliminary testing sequence is briefly described.
A series of in-track wood tie tests were conducted on a yard lead track on a shortline railroad, Transkentucky Transportation, to optimize the in-track installation procedures and to obtain pressure measurements using repeated passes of low-speed locomotives and cars. A normalized pressure distribution was obtained by using metal shims when necessary to fill voids between the ties and pressure cells to insure continuous tie-ballast contact. This test sequence is presented and described.
Additional in-track tests were conducted on Norfolk Southern Railway’s heavy tonnage concrete tie Class 4 mainline with train speeds of up to 64 km/h. Data was obtained for numerous passages of revenue trains over a period of several months for variable weights and types of locomotives and freight cars at typical train speeds. The average pressure intensities at the tie-ballast interface were acquired for six consecutive ties comprising a complete revolution of the wheels. This data is presented and the results discussed.