Determination of the Interaction Parameters of the Soil Containing Geofoam Bead-Geosynthetic Reinforcements

In the last few decades, due to the increasing use of geosynthetic reinforcements in reinforcing the soil, researchers have considered the significance of the behavior of the soil-geosynthetic interface. On the other hand, the use of geofoams in the form of block and/or bead due to a decrease in the weight of the soil mass behind the retaining structures has attracted the designers’ attention. In this regard, the current research was carried out to determine the interaction parameters of soil containing geofoam beads and geosynthetic reinforcements. For this purpose, a large-scale direct shear apparatus with box dimensions of 304.8*304.8*152 mm was used. The used soil was a mixture of Firoozkooh sand (#. 161) and geofoam beads with a diameter of 2 mm and the geofoam mix percentages were selected as 0.2, 0.4, and 0.6 percent by weight of the soil. Also, the reinforcements used in this research included geogrid, geotextile, and geocomposite; accordingly, further analysis and comparison of the obtained results could be possible. According to the results, in the sand-geofoam mixtures reinforced by geosynthetics, upon an increase in the mix percentage of geofoam, shear strength amounts decreased. Also, in these mixtures, the greatest increase in bearing capacity compared to the corresponding unreinforced mixtures was obtained for the samples reinforced with geogrid and also, for samples reinforced with geocomposite and geotextile, respectively. In general, based on the reinforcement type and geofoam mix percentage, an increase in the bearing capacity of the reinforced mixtures with respect to unreinforced mixtures was about 12% to 135%. By increasing the mix percentage of geofoam from 0.2 to 0.6, the amount of this increase was reduced. In the sand-geofoam mixtures reinforced by geosynthetics, the highest value of the interaction coefficient was obtained in the samples reinforced by geogrid, geocomposite, and geotextile, respectively. In the sand-geofoam mixtures reinforced by geogrid, the highest value of the interaction coefficient was observed in the geofoam of 0.4% and then, in the geofoam of 0.2%‌.