Investigation of railway track subgrade. Part 2: Case study

Track quality indices, continued track component performance and subsequent maintenance are highly dependent upon trackbed stiffness. This is exacerbated by consolidation and settlement of subgrade and the subsequent differential track geometry. Consequently, any site investigation to diagnose the causes of track geometry deterioration should include an assessment of stiffness parameters. In addition to stiffness assessment, a trackbed investigation should comprise a full assessment of ballast, sub-ballast and subgrade condition. If information about any of these layers is omitted, a complete diagnosis is not feasible, and consequently appropriate ground improvement schemes may not be implemented. Test devices suitable for trackbed investigation to assess the causes of track settlement have been identified in a previous paper in this series. This paper summarises the staged trackbed investigation performed at a site historically requiring high maintenance, suspected as being caused by poor subgrade. The paper concludes with a diagnosis of the site and suggested remedial schemes deemed suitable for generic treatment of poor subgrade sites.