Composite Resilient Modulus of Geogrid Stabilized Pavement Foundation

Laboratory-based repeated load triaxial testing (a.k.a., resilient modulus or M_r testing) has been widely used for characterizing pavement unbound materials consisting of different mineral compositions, gradations, angularities, and other index properties, fines and moisture contents, and other variants. The M_r testing is usually conducted on a small cylindrical specimen by applying confining pressures and repeated axial stresses, mimicking the possible stress stages due to traffic. However, it is challenging to truly represent the actual field condition in the laboratory due to the absence of all bound and unbound pavement layers forming a pavement system, and due to the presence of a thick, extremely stiff, and unyielding base plate of the cylindrical specimen. As such, the M_r measured in the laboratory may not directly correlate with the M_r measured in the field. An Automated Plate Load Testing (APLT), a field-based plate load testing system for applying dynamic loads and measuring permanent and resilient deformations, offers an opportunity to close a gap between lab and field measured M_r. This paper aims to evaluate composite resilient moduli of geogrid stabilized pavement foundations measured through the APLT system. APLTs were conducted on several test sections consisting of different aggregate base course (ABC) thickness, ABC material types, geogrids, and subgrade conditions. A series of regression models were developed to predict a composite resilient modulus based on ABC thickness, subgrade stiffness, and other parameters. The regression model using the independent variables ABC thickness, subgrade CBR, gradation parameters D50, D85, and % fines performed better than the other models.