Geogrid stabilization in ballasted trackbed for high-speed railways

Ballasted tracks are widely constructed worldwide both for normal, high-speed, and heavy haul railways, which consist of large amounts of diverse-sized gravel particles for a ballast layer of approximately 30 cm just below sleepers. With the increase in in-service time, various distresses, such as particle breakage, ballast fouling, hardening ballast bed, and excessive settlement occur. To clarify the occurrence and evolution mechanism behind these distresses and explore relevant countermeasures, element, model, and field tests have been extensively conducted in last decades, as well as numerical approaches. Geogrid that developed in geotechnical engineering region was found effective in constraining ballast movement and reducing particle breakage in railway engineering. The stabilization effect had also been extensively investigated by element tests and Discrete Element Method (DEM). However, the optimal location of paving geogrid in ballast layer remains unclear to date. Inspired by reproducing the service condition of ballast layer and verifying the obtained results from laboratories, several reduced-scale and full-scale model apparatuses were developed worldwide. One typical apparatus of them established in Zhejiang University has the capacity to mimic the actual train load up to the maximum train speed of 360 km/h and axle load of 30 tons, by which the effect of geogrid on ballasted track stabilization was further validated. It was found that the settlement of the ballast layer was reduced by more than 40 % as a triaxial geogrid was installed at the bottom of the ballast layer. Moreover, the vibration of ballast was significantly decreased even 15 cm above the geogrid. Afterward, field tests were conducted with the same triaxial geogrid installed at the bottom of the ballast layer, notable settlement and vibration reductions effectively proved the stabilization effect of the geogrid. In short, through an overall review on the development and application of geogrids for ballasted track stabilization, these discussions would contribute to a more comprehensive understanding of the internal stabilization mechanism and an efficient application in practice in future.