Pullout Resistance of Steel Geogrids with Weathered Clay as Backfill Material
The pullout resistance of welded steel geogrid reinforcement embedded in poor-quality, cohesive-frictional backfill material such as weathered clay was investigated. Laboratory pullout tests were conducted on various reinforcement sizes, mesh geometry, and compaction conditions of the backfill material. Field pullout tests were also conducted to investigate the pullout resistance of reinforcements embedded at representative overburden, field moisture, and density conditions. The soil-reinforcement interaction indicated the dominant role of passive or bearing resistance contributed by the transverse members to the total pullout resistance. The frictional resistance of the longitudinal members was found to contribute only about 5 to 15% of the total pullout resistance. It was observed that the reinforcement moved nearly as a rigid body and that the pullout resistance along the reinforcement is uniformly mobilized. The field pullout test provided higher pullout resistance compared to that of the laboratory test. Comparison of the predicted pullout bearing resistance with the observed data indicated that the prediction based on the bearing failure model formed the upper boundary while the prediction associated with the punching failure model provided the lower boundary. An empirical equation was proposed to predict the bearing resistance of the transverse members with reasonable accuracy.