Vertical Track Stiffness as a New Parameter Involved in Designing High-Speed Railway Infrastructure

Abstract

The criteria currently employed for the design of railway infrastructure on ballasted track are based on the elements of the superstructure, traffic, and bearing capacity of the subgrade. In high-speed railway, the elements of the superstructure are relatively well defined because they are based on existing experience. The category of traffic is a variable that has an influence from the point of view of the number of axles, weight per axle, and speed; i.e., it is determined a priori, depending on the operating characteristics of the line in question. The third and last point refers to the quality of the subgrade that is based on the values of the California bearing ratio test. The quality of the subgrade has a considerable influence on the behavior of the track that manifests itself in the value the deformation and settlement takes, which is caused to the rail on the passage of traffic. This is attributable to the relationship between the vertical track stiffness and the quality of the subgrade. In turn, this deformation determines the value of the dynamic overloads that are transmitted to the track and consequently its deterioration. Therefore, it would be convenient to introduce a new indicator that is related to the quality of the subgrade: the vertical track stiffness value. This paper deals with the variation in the value of the vertical track stiffness parameter as a function of different types of substructure, presenting graphs and formulations that can be used in the infrastructure design of the rail track. Mathematical expressions to obtain the vertical track stiffness as a function of the height of embankment and the modulus of elasticity of the embankment and the natural ground are obtained from the graphs and a methodology for designing the type of ground used in each layer of the infrastructure is proposed. This methodology is applied to several examples to point out that the application of these tools are of special importance in the case of high-speed lines, where it is necessary to adjust the value of the vertical track stiffness owing to the large effect it has on the value of dynamic overloads generated by unsprung masses.