Performance-based Trackbed Structural Design and Analysis Utilizing Kentrack

The design and construction of the trackbed support structure is extremely important for controlling track settlement, dynamic deflection, and the overall quality of the trackbed. These factors largely influence the long-term performance of the track relative to maintaining adequate geometric features for efficient and safe train operations. Performance-based design methods provide design criteria to assess the relative effects of various factors affecting long-term performance of different trackbed designs. These designs involve, in large part, selecting layer thicknesses and constituent materials possessing various properties inherent to influencing long-term track performance. By using a performance-based design method, it is possible for designers to select trackbed support layer thicknesses and constituent materials to satisfy roadbed performance requirements. Specifically, by considering each layer’s fatigue life related to the number of trains and tonnages, a method is available for designing thicknesses of the various layers and selecting materials according to the importance of a particular section of track. Thus, the predicted design life for various design criteria can be determined. Layer-elastic, finite-element computer programs are available for performance-based structural design and analysis of railway trackbeds. This paper utilizes the KENTRACK design program to illustrate the effects of varying axle loads, subgrade resilient modulus, and layer thicknesses on the fatigue lives of the various layers. The service lives of the subgrade and asphalt layer are predicted by damage analysis. KENTRACK allows users to select individual trackbed layers and associated thicknesses to satisfy roadbed performance requirements. In addition, users may performance-rank different track sectional designs based on the relative importance of the particular track section and the track type.