The use of geogrids  in road and railway projects is becoming an important practice all around the world for solving many design and construction problems. Reinforced granular material is a composite material which combines two different materials in such a way to improve its mechanical properties. However, there is still a lack of the understanding how the geogrids contribute to the observed increase of the load bearing capacity. To allow for  better assessment of the composite behaviour, a series of largescale triaxial tests were conducted on unreinforced and reinforced  gravel  specimens of 50cm in height and 23cm times 23cm in cross-section, using an apparatus developed at the Institute of Industrial  Science, University of Tokyo (Anh Dan et al. 2006). In addition to the variation of the cell pressure, the test series also includes the variation of geogrid types.