Experimental Investigation of Response of Different Granular Soil–3D Geogrid Interfaces Using Large-Scale Direct Shear Tests

Abstract

This paper investigates the effect of reinforcement forms on the interface shear strength of geosynthetic-reinforced granular soil by conducting a set of large-scale direct shear tests. Three sands of different size (fine, medium, and coarse) and fine gravel of particle size between 0.075 and 10 mm were used for the study. Planar and three-dimensional (3D) geogrids of triangular and rectangular forms were adopted as the reinforcing material. The tests were performed at three different normal stresses of 100, 150, and 200 kPa. The interface shear-strength parameters of different granular soil–reinforcement interfaces were quantified in terms of interface friction angle, apparent cohesion, and interface shear-strength coefficient. The effect of position of the 3D geogrid in the upper or lower shear box on the interface shear behavior was also studied. The tests results show that 3D geogrid–reinforced soil provides higher interface shear-strength coefficients compared with unreinforced and planar geogrid–reinforced soil. The highest interface shear-strength coefficient was observed with 3D geogrid–reinforced medium sand (1.25), which shows minimum unreinforced shear strength. It was also observed that the interface shear-strength coefficients were higher for 3D geogrids with rectangular form compared with the triangular form. The results of the present investigation encourage the usability of 3D geogrids in reinforced soil structures.