Elastic Modulus of Geogrid-Reinforced Sand Using Plate Load Tests

An experimental study was conducted to evaluate the elastic modulus of sand reinforced with polymeric geogrids. A total of nine plate load tests were performed in the laboratory using a 1.52 m × 1.52 m × 1.37 m (length × width × depth) test box, and a 0.3 m square test plate. The measured test data were used to evaluate a modulus constant (E₁), rather than the bearing capacity, as traditionally presented in literature. The modulus constant was estimated based on two deformation levels of 9.2 mm and 4.6 mm. These deformation levels, defined as δ₁ and δ_0.5, correspond to normalized settlement ratios (δ/B) of 1.5 and 3.0%, respectively, where B = width of the test plate. In general, a stiffer load-settlement response was measured when the geogrid reinforcement was included. Using SR1 geogrids with sand, the modulus constant (E₁) decreased as a function of increasing u/B ratio (u = distance from plate to Eop reinforcement layer). In comparison, results indicated the presence of a critical u/B ratio when the SR2 geogrids were used. In this study, this particular ratio was estimated to be 0.65. Values of E₁ from large scale model testing by Adams and Collin (1997) correlated well with E₁ values evaluated from this testing program.