Quantifying the Effectiveness of Methods Used to Improve Railway Track Performance over Soft Subgrades: Methodology and Case Study

Abstract

This paper presents a methodology for quantifying the effectiveness of different methods used to improve the railway track performance on soft subgrades. This methodology consists of quantifying the changes in track stiffness from vertical track deflection (VTD) measurements taken before and after the track was upgraded, and the evaluation of the roughness of the track that has developed since the track was upgraded. A case study is presented to explain the steps of this methodology. These upgrades consist of changing the rail from 49.6-kg/m (100-lb/yd) bolted rail to 57-kg/m (115-lb/yd) continuously welded rail (CWR), embankment reconstruction, and using a layer of geogrid at the subballast–subgrade interface. The results of the study show that the VTD measurements are capable of measuring changes in track deflection, and thus modulus, due to the upgrading of the track structures with a high enough resolution to distinguish between the differing test sections. The track geometry measurements suggest that not enough time or train traffic had passed to degrade the track geometry to a level that would start indicating issues in performance. The paper also evaluates the relative effectiveness of the different remediation methods at this study site. Replacement of jointed rail with heavier CWR significantly increased the track stiffness, more so than excavation of the subgrade and reconstruction of the embankment. The combined effect of CWR and the substructure upgrades further improved the track modulus. The geogrid can be used with CWR to reduce the amount of subballast required without an increase in track deflection.