Investigation of railway track subgrade. I: In-situ assessment

Recent research has shown that there is a discernible relationship between trackbed stiffness and track quality deterioration. Even though correlations between maintenance, track geometry deterioration and subgrade condition have been identified, the trackbed is rarely considered in the design and implementation of maintenance and renewals works proposals. Often track components are maintained or replaced with little regard for subgrade properties and their subsequent effects on continued total asset life. Consequently, a need has arisen for a more consistent, detailed trackbed investigation that can be carried out under the physical working and access restrictions applicable in the UK railway network. Level 1 evaluation refers to the assessment of large track lengths, and is concerned mainly with the initial identification of poor subgrade sites. Level 2 evaluation focuses on the causes of track geometry deterioration at identified poor subgrade sites. This paper presents a critical analysis of test devices for identification and assessment of existing and potential subgrade problems, and of their application in a railways environment. Devices deemed potentially applicable were tested on a site on the existing railway network, and the results are presented in part II of this series of papers.