Lateral restraint is considered to be a primary mechanism of geogrid base stabilization, and the geogrid-aggregate interlocking establishes the stiffness enhancement around the geogrid. This paper introduces an innovative application of bender elements in an aggregate base as shear wave transducers to quantify local stiffness increase in the vicinity of a geogrid. Several triaxial test specimens of granite aggregate compacted at optimum moisture content were prepared for resilient modulus testing. For the geogrid-stabilized specimens, a triangular aperture punched and drawn geogrid was placed at mid-height of specimen. To measure shear wave velocities across the specimen at different locations above the geogrid, three bender element pairs were installed on the membrane at three different heights above the mid-specimen. Shear wave velocities and axial resilient strains were recorded under the applied stress states. The shear moduli obtained from the geogrid-stabilized specimen were always greater than those obtained from the unstabilized specimen thereby presenting a local stiffness improvement due to geogrid-aggregate interlocking. Further, in the stabilized specimens, the shear moduli obtained near the geogrid were always greater than those obtained far from the geogrid. Therefore, through the successful shear wave velocity measurements and shear modulus estimation, bender element pairs can be effectively used for the quantification of local stiffness improvement due to geogrid-stabilized aggregate.