Two test methods have been developed in this project. The first test method is a compression test of a cylinder constructed out of geogrid material and filled with crushed stone. This test is simple and can be easily performed. Only a compression loading machine is needed for this test. The sample preparation is straightforward. However, multiple tests must be run to analyze geogrids with different ultimate tensile strength or different grid aperture size on machine direction and cross machine direction. The second test method is Geogrid Bearing Ratio (GBR) test. This test was developed to measure the effect of geogrids on bearing capacity improvement. The ratio of bearing capacity for the with geogrid treatment to the bearing capacity for the without geogrid treatment is an index that captures a geogridβs contribution to bearing capacity improvement. The GBR test result is one-parameter, which informs designers of how a geogrid functions in the pavement structure. This test enables comparisons of geogrids with differently aperture shapes. Any difference on grid single string strengths or aperture sizes or shapes are identified by GBR number. GBRs are related to the combined function of string strength, rigidity and integration properties of the geogrid. The optimal geogrid installation position under penetration loading is explored using GBR test. The optimum position is at 4 in. from bottom in 8 in. thick crushed stone configuration under 1.954 in. in diameter piston loading. It is critical to analyze or test particular cases in order to determine a practical, optimal design
