Full-scale model tests on ballasted tracks with/without geogrid stabilisation under high-speed train loads

High-speed trains running on ballasted tracks intensify the vibration of ballast layers to a greater extent than conventional passenger trains, with detrimental effects to train operations. The stabilisation effect of the geogrid in real railways under high-speed train moving loads remains unclear. Herein, full-scale model tests on a ballasted trackbed with and without geogrid were conducted, and a novel sequential loading system was adopted to apply the train moving loads. The highest train speeds were 300 km/h for the ballasted track without geogrid, and 360 km/h for the ballasted track with geogrid. To monitor the geogrid tension strain, distributed fibre Bragg grating sensors were mounted on the geogrid ribs. It was found that the maximum geogrid tension strain between neighbouring sleepers was six times larger than that beneath the sleepers. The geogrid influence zone in the ballast layer was identified as being at least 15 cm above the geogrid. The dynamic stress on the subballast surface was decreased by about 49% in the stabilised trackbed. The testing results also showed that geogrid stabilisation could reduce ballast breakage from 14·9% to 2·5% and reduce the permanent settlement of ballast layer by 40%. The experimental results presented in the paper provide a benchmark for geogrid-stabilisation modelling and will be referenced for the optimal design of ballasted tracks.