Advances in Ground Improvement and Principles of Track Geomechanics for Future Railways
The need for transport infrastructure to perform for long periods of time is best shown by the way heavy haul transport networks are expected to withstand higher speeds and heavier axle loads. Ballasted rail tracks are one of the major transport systems that cater for passenger and heavy haul freight trains, but despite this advantage, geotechnical challenges such as ballast breakage, poor drainage of soft subgrade, fouling (e.g. coal and subgrade soil), pumping of clayey subgrade, differential track settlement and track misalignment due to excessive lateral displacements increase the cost of track maintenance. This means that soft deposits and problematic subgrade must be stabilised before constructing any infrastructure to prevent unacceptable differential settlement. Several ground improvement techniques are already in use, of which Prefabricated Vertical Drains (PVDs) combined with surcharge and vacuum preloading has proven to be an efficient, cost effective and popular technique for accelerating consolidation. Moreover, energy-absorbing materials manufactured from waste tyres, such as ballast mats, under sleeper pads, rubber crumbs, and tyre cells also help to attenuate dynamic train loads and vibration. These devices not only mitigate ballast degradation and deformation, they also improve track stability and increase longevity. Recycling waste materials not only helps to solve geotechnical issues, it is also economically beneficial and environmentally sustainable.