Design of ballasted railway track foundations using numerical modelling. Part I: Development

In this paper, a new design method is developed for ballasted railway track foundations that must support high-speed trains and heavy axle loads. The proposed method is intended to prevent the two most common track failures; namely, progressive shear failure of the track subgrade and excessive plastic deformation of the track substructure (i.e., ballast plus subgrade). The method is based on improved empirical models and sophisticated three-dimensional (3D) finite element (FE) numerical analysis. The improved empirical models are used for predicting the cumulative plastic deformation of the track, whereas the stress parameters of the ballast and subgrade layers are obtained from the 3D FE numerical analysis. The outcomes are then synthesized into a set of design charts that form the core of the proposed design method so that it can be readily used by railway geotechnical engineers for routine design practice. The design method can be applied to various practical conditions of train–track–ground systems, including the modulus, thickness, and type of ballast and subgrade. In addition, the traffic parameters that have a significant influence on track performance are also considered in the design method, including the wheel spacing, train speed, and traffic tonnage. The new design method has significant advantages over the existing methods and would provide a major contribution to modern railway track design and code of practice. The applications of the new design method are presented and explained in a companion paper (i.e., Part II: Applications).