عنوان مقاله [English]
Cost-effectiveness, fast performance, and relatively long service life have made geosynthetics widely used in geotechnical structures such as road pavement, retaining walls, slope stabilization and foundations, bridge abutments, embankments or at the boundary between embankments and subgrade to be used. The soil geocomposite used in this research, which is made in Iran under the brand name of GC Soil 40/40, is a combination of geogrid and geotextile and is used in various projects such as embankment bed reinforcement and separation to implement embankment on fine and loose subgrade. In general, in the design of geosynthetics, including soil geocomposites, interaction mechanisms including slip and pullout as well as interaction coefficient between soil and geosynthetic should be considered. Accordingly, to evaluate the soil-geocomposite interaction, direct shear and pullout tests were performed in one-layer soil (sand-geocomposite and gravel-geocomposite) and two-layers soil (sand-geocomposite-gravel) under different vertical stresses. The results of direct shear tests showed that reinforcing the soil with geocomposite reduced the angle of friction and increased soil adhesion. Despite the increase in shear stress and pullout resistance with increasing vertical stress, the interaction coefficients decrease with an increase in the vertical stress. This issue can be related to the nonlinear behavior of pullout force and soil-geocomposite shear stress with vertical stress. Vertical stress is an effective factor to increase the pullout resistance and type of mode geocomposite rupture and also has a significant effect on the displacement at the maximum pullout resistance. The results showed that under the same loading conditions, the placement of the geocomposite on the common surface of the two layers soil changes the pullout behavior compared to the one-layer soil. In general, it can be stated that the soil-geocomposite interaction, in addition to vertical stress, is sensitive to the type and size of soil particles, one- and two-layers of soil. For sand-geocomposite and gravel-geocomposite interfaces, the average coefficients of interaction(𝑐𝑖 ) for direct shear are 0.8 and 0.91, respectively. Also, the average pullout interaction coefficients(𝑓𝑏) for sandy and gravel soils reinforced with geocomposite (one-layer) are 0.35 and 0.47, respectively, and this coefficient is obtained as the average of 0.51 for sand-geocomposite-gravel (two-layer).