Scale effect on the behaviour of geogrid-reinforced soil under repeated loads

One of the most useful geosynthetics in soil reinforcement is geogrid due to its high tensile strength, having a great influence on soil skeleton reinforcement and eventually, increasing bearing capacity of the foundation. In this research, a series of 36 repeated plate load tests have been carried out to investigate the scale effect on geogrid-reinforced soil, tending to further understanding of the behaviour of geogrid-reinforced soil system. Four different soil grains sizes, two different geogrid's aperture sizes (with roughly the same tensile strength) and three different loading plate sizes are the variables considered. During the tests, the applied loading and soil surface settlements were recorded to evaluate the systems' response. As it was expected, the reinforced soil exhibited higher bearing capacity than the unreinforced status, up to 635%. The results show that increasing loading plate size and soils' particle size fortify the response of foundation, especially in reinforced status, against the loading plate penetration. The results further focused on the important role of scale effect on the response of reinforced foundation. It was understood that the optimum nominal aperture size of geogrids should be about 4 times of medium grain size of soil. Also, it was found out that in order to acquisition of highest reinforcement benefits, the footing's width should be in the range 13–25 (20 in average) times of medium grain size of the backfill. Finally, to achieve the best results, it is recommended that the aperture size of geogrids should be selected roughly 0.2 times of footing width.