Track stiffness considerations for high speed railway lines

This chapter discusses the importance of the vertical track stiffness as a means to guide high speed railway track bed design and inform decisions regarding track maintenance and renewal. To this end, a rational approach to substructure track-bed design is described which it is hoped will facilitate appropriate track design and enable the adaptation of existing design procedures to provide a realistic design for the conditions at hand. Despite adopting suitable design and construction standards, however, a number of factors may still cause the track stiffness to vary spatially. Sometimes the stiffness variation may be very large within a short distance. These are likely to cause variations in the wheel/rail interaction force and will have a detrimental effect on track degradation increasing wear, fatigue of track components, and track settlement. This chapter discusses these issues and describes the use of numerical models to; assess the influence of track stiffness variations on the wheel/rail contact force, and; investigate the use of possible countermeasures. Techniques which have been developed to measure track stiffness, including the novel approach developed by one of the authors, are described, and the possible uses of such measurements to make appropriate and timely railway maintenance and renewal decisions are discussed. Devices from different countries are described in relation to the evolution from static to rolling devices capable of effecting measurements at train speeds. Such techniques have undergone a process of continual evolution in recent years and several are now ready to be developed from research tools to those capable of being used practically by commercial organisations.