Investigation into some design aspects of ballasted railway track substructure

Due to the daily congestion of highways, railways have become the most popular means of public transportation, which increased the demand for heavier and faster trains while keeping the cost of track maintenance at its minimum level. This requires an investigation into the effect of various design factors on the overall track performance. Such an investigation is very important for railway geotechnical engineers to arrive at optimum track design and maintenance. Ballasted railway track substructure consists of graded layers of granular media of ballast and sub-ballast (capping) placed above compacted subgrade. Conventional methods for design of ballasted railway track substructure are based on simple theoretical or empirical solutions that assume a homogeneous half-space for all track layers and neglect the individual properties of each layer. This results in overestimation of the vertical pressure distribution with depth, leading to incorrect estimation of track thickness (i.e. ballast and sub-ballast). In addition, most available methods assume linear elastic behaviour for substructure materials. In order to conduct more realistic multilayer simulations including material elastoplasticity, the more complex numerical solutions using the finite element method can be used. In this paper, two-dimensional versus three-dimensional finite element analyses using PLAXIS are carried out to investigate the validity of the simpler two-dimensional solutions. Furthermore, an elastoplastic constitutive model that represents more actual characteristics of track substructure materials is used and compared with the simpler elastic model. Detailed modelling of the track components including rail, sleepers, ballast, sub-ballast and subgrade is presented and the results are discussed.