Roadbed Degradation Mechanism under Ballastless Track and Its Countermeasures

This paper investigates the degradation of roadbeds for ballastless track as well as supplying countermeasures. Such degradation often occurs in those beds where the soil is predominately made up of clay or clay-like materials after heavy rainfall or other types of water inundation. The strategies against this type of degradation are underpinned by three main concepts: decrease the dynamic water pressure on the roadbed, decrease pore water level in the roadbed, and increase the roadbed soil cohesion. More pragmatically, these policies took the form of a water-pressure diffusion method where a permeable layer is set between the grouted layer and the roadbed, and the Bentonite liner for track-bed surface (BLITS) where the BLITS layer is placed between the grouted layer and the ballast penetration layer. The authors conclude that this type of degradation is local and progressive due to the outflow of the fine-grain part of the roadbed. Although mud pumping is sometimes useful in this circumstance, roadbed improvement is required for long-term sustainability.