Uniaxial GEOGRID Pullout Mechanism Characterization from Calcareous Sand Backfill
There are two primary failure mechanisms associated with Reinforced Soil Systems (RSS) walls using geogrids including rupture and pullout. The failure mechanism with relevance to this research is the pullout failure. This type of failure mechanism depends on the interaction between the backfill soil and reinforcement. In order to select a type of backfill soil or reinforcement that will provide sufficient interaction strength, the soil reinforcement interaction should be tested and characterized using pullout tests. Siliceous sands have been widely used as a backfill soil in MSE walls. Also, most published researches addresses the geogrid pullout resistance embedded in siliceous sands. geogrid pullout design empirical equations and parameters in design codes such as AASHTO are based on using siliceous sand as a backfill material. In this paper, the aim is to evaluate the interaction between calcareous sand as a backfill soil and two types of geogrids including High Density Poly Ethylene (HDPE) and polyester, performing and analyzing laboratory pullout test results. Pullout tests were performed at vertical stresses of 100, 150 and 200 kPa corresponding to approximate wall heights of 5 to 11 m. The results of pullout test are used to define geogrid pullout resistance parameters from calcareous sand. The results of this study show that: (1) Pullout resistance force for HDPE geogrid embedded in siliceous sand are higher than those embedded in calcareous sand by 17%, (2) Pullout resistance force for polyester geogrid embedded in calcareous sand are higher than those embedded in siliceous sand by 6%, (3) The pullout resistance factor for polyester geogrids embedded in calcareous sand is greater by 4% than the same factor for geogrids embedded siliceous sand. However the pullout resistance factor for HDPE geogrid embedded in calcareous sand is smaller by 16% than the same factor for geogrids embedded in siliceous sand.
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