Investigating the reinforcement effect of geogrids in flexible pavements

Geogrids have been increasingly used to reinforce granular base course to improve the performance of flexible pavements. In this study, different interfacial behaviors of geogrid-reinforced aggregate were investigated through laboratory experiments. Influence factors affecting the reinforcement effect were analyzed, and reinforcement mechanisms were revealed.Firstly, the repeated load triaxial (RLT) test was conducted to investigate the vertical resilient deformation behavior of the reinforced aggregate. The result show that the RLT test was not effective in evaluating the reinforcement effect. To further analyze the lateral resilient deformation behavior of the reinforced aggregate, a large-scaled cyclic shear test was introduced. The result show that this method could effectively quantify the reinforcement effect of geogrids along with a term, resilient interface shear modulus.Secondly, the interfacial shear behavior of the reinforced aggregate was studied by a large direct shear test. The relative size of aggregate to geogrid aperture had a significant effect on the mechanical properties of the reinforced aggregate and interface failure modes. A guideline to optimize the combination of geogrids and aggregates was proposed based on the results.Thirdly, a modified loaded wheel tester was employed to investigate the permanent deformation behavior of the reinforced aggregate. Critical influence factors affecting the reinforcement effect were analyzed. A better reinforcement effect could be obtained by increasing the portion of effective aggregates, increasing the tensile strength of geogrids. Triaxial geogrids performed better in reinforcing aggregate than biaxial geogrids when their tensile strength were similar. The tensile strength of geogrids had much significant effects on the reinforcement compared to the aperture geometry.Last, the resilient and permanent deformation behaviors of reinforced granular base were further studied through a full-scale accelerated pavement testing to verify the laboratory results. The test program included performance testing, response testing and pavement trench. The result demonstrated that an enough permanent deformation was needed for mobilizing geogrids to constrain the lateral movement of granular particles, increase the modulus of base course, and improve the stress distribution on subgrade. For a pavement system consisting of a thin surface and base layer, a proper placement position of geogrids was at the base-subgrade interface.