1. Introduction -- 2. Track structure and rail load -- 3. Factors governing ballast behaviour -- 4. State-of-the-art laboratory testing and degradation assessment of ballast -- 5. Behaviour of ballast with and without geosynthetics and energy absorbing mats -- 6. Existing track deformation models -- 7. A constitutive model for ballast -- 8. Track drainage and use of geotextiles -- 9. Role of subballast, its drainage and filtration characteristics -- 10. Field instrumentation for track performance verification -- 11. DEM modelling of ballast densification and breakage -- 12. FEM modelling of tracks and applications to case studies -- 13. Non-destructive testing and track condition assessment -- 14. Track maintenance -- 15. Recommended ballast gradations -- 16. Bio-engineering for track stabilisation.
Ballast plays a vital role in transmitting and distributing the train wheel loads to the underlying sub-ballast and subgrade. Bearing capacity of track, train speed, riding quality and passenger comfort all depend on the stability of ballast through mechanical interlocking of particles. Ballast attrition and breakage occur progressively under heavy cyclic loading, causing track deterioration and rail misalignment affecting safety, and also demanding frequent and costly track maintenance. In the absence of realistic constitutive models, the track substructure is traditionally designed using empirical approaches. In this book, the authors present the detailed information on the strength, deformation, and degradation aspects of fresh and recycled ballast under monotonic, cyclic, and impact loading using innovative geotechnical testing devices. A new stress-strain constitutive model for ballast incorporating particle breakage is presented. The mathematical formulations and numerical models are validated using experimental evidence and field trials. The effectiveness of various commercially available geosynthetics for enhancing track drainage and stability is elucidated. Revised ballast gradations are presented for modern high speed trains capturing particle breakage. This book should prove useful for final year civil engineering students and postgraduates, and for practicing railway engineers with the task of modernizing existing designs for heavier and faster trains--