Continuous Vertical Track Deflection Measurements to Map Subgrade Condition along a Railway Line: Methodology and Case Studies

This paper presents the methodology developed for the use of continuous vertical track deflection measurements from a moving loaded rail car to map the subgrade condition along a railway line. This analysis of deflection data was developed following the collection of more than 12,000 km of measurements. It was evident from the collected data that unprocessed deflection measurements are heavily effected by the track surface condition such as joints and geometry irregularities so as to obscure the deflections because of poor subgrade support. A filtering method was employed to minimize the influence of the surface condition which occur at short wavelengths and show the variations in track deflections because of changes in subgrade conditions which occur at longer wavelengths. The resulting processed data are compared with the geology over two study railway subdivisions to demonstrate that the processed vertical track deflection measurements are representative of the subgrade conditions. The filtering process, examples of the effect of track surface on the deflection measurements, and the limitations of the resulting data are also discussed.