Quantifying the effects of geogrid reinforcement in unbound granular base

This study presents an effort to quantify the effects of geogrid reinforcement in the unbound granular base through laboratory testing. Two laboratory tests, the large-scale cyclic shear test and the repeated load triaxial test, were employed. The test protocol of the cyclic shear test was developed by modifying that for the triaxial test. The cyclic shear test was performed by applying a series of cyclic shear stresses to the geogrid-aggregate interface under different normal stresses. Two different types of geogrids were used as reinforcement in unbound granular material. Resilient modulus (M_R) from the repeated load triaxial test and a term named resilient interface shear modulus (G_i) from the cyclic shear test was used to characterize the effects of geogrid reinforcement in unbound granular base, respectively. The results of triaxial tests showed that the inclusion of geogrid had a negligible effect on the resilient modulus, indicating that the triaxial resilient modulus test may not be effective in evaluating the geogrid reinforcement in unbound granular materials. Compared to the triaxial resilient modulus test, the cyclic shear test showed great potential in identifying the effects of geogrid reinforcement, with an obvious improvement in the degree of interlocking between geogrids and aggregates.