Influence of tensile strength of geogrid and subgrade modulus on layer coefficients of granular bases

Abstract

This paper presents a series of large-scale laboratory experiments conducted on pavement sections to evaluate the performance of geogrid-reinforced base layer overlying various subgrade conditions (resilient modulus ranging between 10 MPa and 72 MPa). Four types of geogrids with different tensile strengths, aperture sizes, and polymer types were used to investigate the influence of geogrids on the structural coefficients in terms of modulus improvement factor (MIF) and base layer coefficient ratios (LCRs). Further, a thorough analysis was performed on a three-layer flexible pavement system to propose firstly new models for base layer coefficients (a2u) for control (unreinforced) sections; and secondly, LCR equations and layer coefficient models for geogrid-reinforced base layers (a2r). The experimental results indicate that the stiffness of the subgrade significantly influences the performance of the pavement system. The optimum reinforcement depth was found to be one-third of the base layer thickness measured from the top surface. For an optimum geogrid configuration on a weak subgrade, a maximum LCR value obtained was about 1.8. As-built pavement section of Interstate Highway-8, Arizona, was evaluated to validate the proposed models. Based on the study, limiting values for MIF and LCR for geogrid-reinforced bases were proposed. Finally, a set of design charts were provided to determine the granular layer (base and subbase) thickness for a given subgrade and traffic conditions and a practical range of base layer resilient modulus values (200–400 MPa).