The results of a direct shear and pullout testing program conducted to evaluate the interaction properties of three types of flexible geogrids having 2 cm, 5 cm and 10 cm square apertures within two types of backfill materials are presented. The first backfill material was a 5 cm nominal size tire shred fill and the second backfill material was a rubber-sand mixture consisting of a blend of 5 cm tire shreds and sand. Direct shear testing was conducted using a large direct shear box having plan dimensions of 30 cm by 30 cm and a total depth of 23 cm. Pullout tests were carried out in a large pullout box having plan dimensions of 1.2 m in length by 0.9 m in width and 0.5 m depth. Coefficients of interaction between 0.22 to 0.49 for tire shreds and 0.25 to 0.53 for rubber-sand were calculated.