Laboratory investigation of particle size effects on the shear behavior of aggregate-geogrid interface

As an effective method to explore the interaction mechanism between aggregate particles and geogrids, a large-scale direct shear test was employed to study the shear behavior of aggregate-geogrid interface and the effects of particle size on the interfacial shear strength. Two types of geogrids with rectangular or triangular aperture and three single-sized coarse aggregates, 12.5-19 mm, 19-25 mm, 25-37.5 mm, were tested in this study. Multiple parameters were employed to investigate the reinforcement of geogrids in aggregate, including peak shear strength, residual shear strength, vertical displacement and interfacial shear strength efficiency coefficient, α. Results show that the values of α ranged from 0.78 to 1.01, and the aggregate-geogrid interface of AGG2 achieved the highest α among the three aggregates, indicating that the 19-25 mm aggregate had the best interlocking effect reinforced with geogrids used in this study. The combinations of geogrids and aggregate exhibited different interaction mechanisms and failure modes. Based on the test results, the method was improved for determining the appropriate geogrid aperture size for an aggregate gradation. Effective interlock could be achieved when the ratio of the equivalent aperture size to particle diameter was 1.30-1.71 for biaxial geogrids and 1.08-1.43 for triaxial geogrids.