Soil is an important part of a railway track structure. It provides the foundation for the structure and distributes the imposed loads. Consequently, soil has an influence on the condition of a track structure and a low quality soil can ultimately cause failure of the track structure. To be able to include the condition of a soil in the assessment on track quality, the following research question is posed:
“What is the quantitative influence of soil on the track condition for the railway tracks between Utrecht and Den Bosch?”

To be able to answer the research question, first the influence of soil on track condition is distinguished. The most important failure types, progressive shear failure and excessive plastic deformation, are best characterised by the strength of the soil and the deformation of the tracks respectively. For these characteristics a method is developed, which assesses the track condition. For strength a bearing capacity approach is used and for deformations a beam-on-an-elastic-foundation model is used. The process of the method is illustrated by executing it for a specific trajectory, being the Utrecht-Den Bosch line in the Netherlands. To take into account the variability of different soils, the soil type and some specific soil parameters derived from Cone Penetration Tests are determined and applied in the calculations for the assessment.

From the results can be concluded that for the Utrecht-Den Bosch line, the track quality considering passenger trains will either deteriorate limitedly or not at all. This is the case for quality related to both strength and deformation. For cargo trains, the quality related to deformation is such that limited deterioration can be expected. For strength, however, a large number of sections has a condition varying between the failure level and the desired level, which means that significant deterioration is possible, though, there are sections with higher quality as well.