Pullout Resistance Factors of Metal Strips in Tire Shred-Sand Mixtures

Shredded tires mixed with sand are used as a backfill material for mechanically stabilized earth (MSE) walls and as an embankment fill material. Use of tire shred-soil mixtures as backfill materials in mechanically stabilized earth (MSE) walls has several advantages over other backfill materials: (1) good drainage; (2) high shear strength; and (3) low compacted unit weight. Estimation of pullout resistance of reinforcement embedded in tire shred-sand mixtures is essential for the design of these structures. In this paper, the results of large-scale laboratory pullout tests on ribbed-metal strips in tire shred-sand mixtures are presented. The effects of tire shred size, tire shred-sand mixing ratio and confining pressure on the interaction between the ribbed-metal strip and tire shred-sand mixtures are also evaluated. Three sizes of tire shreds are considered: tire chips (with 9.5-mm nominal size); tire shreds 50-to-100 mm and 100-to-200 mm in length with mixing ratios of 0, 12, 25; and, 100% of tire shreds in the mixtures (by weight). For the test conditions considered in the study, the pullout resistance factors of metal strips placed in sand only ranged from 0.87-1.49, whereas, for tire shred-sand mixtures, this factor ranged from 0.75-1.25, 0.57-1.08, and 0.32-0.54 for the 12/88 mix, 25/75 mix and 100/0 mix, respectively.