Bearing and Frictional Contributions to the Pullout Capacity of Geogrid Reinforcements in Cohesive Backfill

Abstract

The interface resistance between the geogrid reinforcements and cohesive backfills are dependent upon the failure mechanism involved, the properties of the backfill, the test conditions and the geometry and stiffness of the geogrids. In the current study, the results of field and laboratory pullout tests, conducted by Farrag and Morvant, were compared to the pullout resistances predicted using the relationships readily available for calculating the frictional and bearing resistances of the reinforcements. The calculation of the bearing resistances was based on the relation recommended by Peterson and Anderson, whereas the frictional resistances were calculated based on the effective (solid) frictional areas of the geogrids with two interface (shear strength) factors of (0.8 and 1.0). The field pullout tests were conducted in a 20 ft (6 m) high wall constructed at the Pavement Research Facility (PRF) of the Louisiana Transportation Research Center (LTRC), while the laboratory tests were conducted in a test box in the geosynthetic engineering laboratory of the LTRC. Four geogrids were used in this study: Stratagrid-500, UX-750, UX-1500, and UX-1700. The tests were conducted at different levels of stress and different reinforcement lengths. Based on the comparison of the total predicted and the laboratory tests results, the relationship recommended by Peterson and Anderson was found to conveniently predict the contributions of the bearing resistances of the transverse members of the reinforcement. However, the same relationship was found to have more significant errors in predicting the bearing contributions of the pullout strips in the field. The contributions of the bearing resistances to the pullout capacities of geogrids were found to vary from 8% to 40%, depending on the types, geometry and stiffness of the geogrid.