Comprehensive Review on Subgrade Enhancement Techniques for High-Speed Railway Dynamics in the Light of Environmental Concerns

The technological advancements made high-speed railways (HSR) are one of the best emerging modes of transportation and expanding throughout the world because of its enormous benefits. Most populated and large countries like India and China require a very rapid, reliable, and cost-effective transportation means such as HSR. China is already standing first with the largest HSR network in the world, and India is just starting its journey. The design of railway tracks for high-velocity trains is complicated and different from conventional train tracks because static stiffness is considered for designing the normal speed train track–subgrade–ground system, whereas dynamic stiffness needs to be considered for high-speed railway tracks. The HSR tracks require a strong subgrade and natural ground as the dynamic loads of high-speed trains generate huge vibrations that lead to track irregularities. The huge vibrations generated by high-speed railways weaken the track–subgrade system and, in the long run, affect the performance of the HSR. These vibrations drastically increase the settlements whenever the train inevitably passes through the soft soils and mud pumping zones. Differential settlements can happen when the train crosses the soft to hard region or vice versa due to rigidity differences. The occurrence of these situations poses a lot of challenges to HSR safety and passenger comfort. This paper encompasses the possible solutions for ground–subgrade–track improvement. Moreover, the paper considered the environmental concerns of the ground vibrations due to the propagation of dynamic waves of HSR and codal provisions for designing the HSR system.