Horizontal stiffness evaluation of geogrid-stabilized aggregate using shear wave transducers

Abstract Lateral restraint resulting from the interlock between geogrid and aggregate is recognized as a primary mechanism governing the load-bearing behavior of a geogrid-stabilized pavement base course. However, the level of geogrid–aggregate interlock and the local stiffness enhancement due to the lateral restraint has not been adequately quantified. In this paper, a new experimental method is proposed to evaluate the stiffness enhancement provided by the interlock of the geogrid–aggregate composite system using shear wave transducers. Repeated load triaxial tests were conducted to determine the resilient modulus and deformation characteristics of both geogrid-stabilized and unstabilized base course aggregates. The stabilized test specimens were evaluated for two geogrid types with rectangular and triangular apertures. For the shear wave measurements, three pairs of bender elements fixed at each mounting base were installed diametrically on the triaxial test specimens at three different locations above the mid-height level, where the horizontal shear modulus profiles of the geogrid-stabilized and unstabilized specimens were determined. The experimental results indicate that the shear modulus profiles obtained as a function of confinement changed significantly based on the geogrid inclusion and type, whereas there were no considerable changes in the resilient moduli from the different specimens, as they were only influenced by the applied stress states. The shear moduli estimated in the vicinity of the geogrid were greater than those at locations farther away from the geogrid, which was installed at the mid-height of the specimen. The shear modulus profiles varied according to the confining stress, and the shear modulus ratio of the stabilized to unstabilized specimens clearly demonstrated the stiffness enhancement provided by the two different geogrids. Accordingly, the shear modulus profiles estimated from the horizontal shear wave measurements of the bender element can be effectively used to determine the mechanically stabilized layer characteristics of a geogrid, and therefore quantify the local stiffness enhancement provided by the geogrid–aggregate interlock.