Bender Elements Successfully Quantified Stiffness Enhancement Provided by Geogrid-Aggregate Interlock

Lateral restraint is a primary mechanism of geogrid base reinforcement contributing to the performance improvement of flexible pavements, and the interlocking between the geogrid and aggregate is responsible for stiffness enhancement in a zone formed around the geogrid. A novel application of bender elements is introduced: as shear wave transducers for quantifying local stiffness increase in the vicinity of a geogrid. Several triaxial test specimens of a dense-graded granite-type aggregate were prepared at two moisture contents for resilient modulus testing. Reinforced specimens also included a punched and drawn geogrid piece placed at specimen midheight. Two pairs of bender elements installed on the membrane at two heights enabled measurement of shear waves horizontally across the specimen. Shear wave velocities and axial resilient strains were recorded under the applied stress states. The test results show that the resilient modulus of the reinforced specimen was similar to that of the unreinforced one tested at the same moisture content. In contrast, the shear moduli obtained at midheight of the reinforced specimen were always greater than those obtained from the unreinforced specimen, indicating a local stiffness increase in the vicinity of the geogrid. In the reinforced specimens, the shear moduli obtained near the upper end were always less than those obtained from the specimen midheight. The small-strain shear modulus determination by bender elements was effective for evaluating the stiffness enhancement provided by geogrid-aggregate interlock.