Discrete element modelling of cyclic loads of geogrid-reinforced ballast under confined and unconfined conditions

The discrete element method has been used to simulate cyclic loading of geogrid-reinforced ballast under confined and unconfined conditions. For the confined condition, box tests have been simulated on unreinforced samples and reinforced samples with different geogrid positions and geogrid apertures. The response of the ballast layer reinforced with geogrid under repeated loading agrees with experimental results. It was found that the optimum location of geogrid is 100 mm depth from base, and the triaxial geogrid outperforms biaxial geogrid. For the unconfined condition, cyclic loading of a trough of ballast (the Composite Element Test (CET) devised by Brown et al. (2007)) has also been simulated, and the sample with the geogrid at 50 mm from the sub-ballast layer performs better than that at 100 mm or 150 mm from the sub-ballast. It was also found that the used of two geogrids at both 50 mm and 150 mm from the sub-ballast gave smaller settlement than using a single layer geogrid, or the unreinforced ballast. However the double-reinforced ballast performs only marginally better than the sample reinforced 50 mm above the sub-ballast. The geogrid reinforcement limits the lateral displacement in reinforced zone, which is approximately 50 mm above and below the geogrid. (C) 2012 Elsevier Ltd. All rights reserved.