عنوان مقاله [English]
The behavior of reinforced soil structures is largely governed by interaction mechanisms that develop between the reinforcement inclusions and fill material. Because of the variety of influential factors, the complex interaction mechanisms between soil and reinforcements are still far from clear. Different experimental methods, including direct shear and pullout tests, have been used to identify and improve the understanding of soil-reinforcement interaction. In the current research, pullout tests were used to evaluate soil-geogrid interaction through relative soil-reinforcement movements during pulling out of the reinforcement. In this regard, large-scale pullout tests (i.e., 100 x 60 x 60 cm) were carried out on samples reinforced with an HDPE geogrid, while
digital images of deformed soil in close vicinity of the geogrid were captured and image processing was applied using particle image velocimetry (PIV) methods. Employing GeoPIV program, successive pairs of photographs were compared to determine the incremental values of displacements and strains at soil-reinforcement contact surfaces during pullout test. Samples were subjected to normal pressures of 25, 50 and 100 kPa. Two sandy and gravely soils of different particle sizes were used in the study for the preparation of samples to assess the influence of grain size on soil-geogrid interactions and the relative displacements. According to Unified Soil Classification System (USCS), sandy soils were classified as SP and SW and the gravely soil as GP. Results of the investigation showed that soil particles in close vicinity of transvers ribs are displaced in a circular manner, and the thickness of the
shear band around the geogrid increases with the increase in grain size. Punching shear failure mechanism was found in SP soil, while general shear failure mode was observed in SW and GP soils during pulling out of the reinforcement. Also, with the increase in grain size, asymmetrical shapes of shear band change to symmetrical shapes.