REPEATED LOADING OF REINFORCED FINITE DEPTH GRANULAR MATERIAL

Granular track supports built over compacted clay or silt subgrades are often susceptible to excessive settlement failure due to lateral spreading of the ballast, initiated by the seasonal softening of a thin upper layer of the subgrade. The inclusion of geosynthetic geogrid reinforcement within the granular support is investigated as a method of reducing the settlement of these structures. The investigation was conducted in the laboratory using a small-scale model of a track-ballast system overlying artificial subgrades of different compressibilities, including a rigid subgrade. The model was subjected to a program of repetitive loading, using a cyclic load that returned to zero at the end of each cycle. The performance of test configurations reinforced with a single layer of geosynthetic geogrid was compared with unreinforced configurations. When placed at the optimal depth, the geosynthetic geogrid reduced the rate at which accumulated plastic settlements were generated for all the subgrade conditions.