Tire Shred Backfill in Mechanically Stabilized Earth Wall Applications

Tire shred-soil mixture backfill for use in mechanically stabilized earth (MSE) walls has several advantages over traditional backfill materials: 1) good drainage, 2) high shear strength, 3) low compacted unit weight and 4) low lateral pressure exerted on retaining structures. This work presents the results of laboratory tests performed on tire shred-sand mixtures focusing on determining the properties required for their use as backfill in MSE wall applications. Three sizes of tire...
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Tire shred-soil mixture backfill for use in mechanically stabilized earth (MSE) walls has several advantages over traditional backfill materials: 1) good drainage, 2) high shear strength, 3) low compacted unit weight and 4) low lateral pressure exerted on retaining structures. This work presents the results of laboratory tests performed on tire shred-sand mixtures focusing on determining the properties required for their use as backfill in MSE wall applications. Three sizes of tire shreds are considered: tire chips with 9.5mm in nominal size, and tire shreds with 50-to-100-mm and 100-to-200-mm in length. The optimal mix proportions of tire shred-sand mixtures for enhanced mechanical response of the composite material are provided. Segregation of the materials in the tire shred-sand mixtures was investigated for various mix proportions. The effects of tire shred size, and tire shred-sand mixing ratio on the interaction between geogrids/ ribbed-metal strips and the mixtures are evaluated based on a series of laboratory pullout tests. Results indicate that the optimal mix proportion of tire shreds and sand is 25/75 and 30/70 (tire shred/sand) by weight, equivalent to approximately 40/60 and 50/50 (tire shred/sand) by volume for tire shreds with 50-100 mm and 100-200mm in length, respectively. This optimum mix proportion also ensures negligible segregation of the components of the mixture in the composite material. For all three shredded tire sizes considered, the pullout capacity of a geogrid embedded in the tire shred-sand mixtures prepared at the optimum mixing ratio is larger than that obtained for pure tire shreds. The pullout capacity of geogrid placed in samples prepared at optimum tire shred-sand mixing ratio is found to be higher for tire chip-sand mixtures than for tire shred-sand mixtures. This is mainly due to the crossing of the geogrid by the tire chips, which generates passive resistance during pullout. The size of tire shred has a negligible effect on the pullout response of ribbed-strip embedded in mixtures. Large-scale direct tests evaluated the shear strength properties of samples prepared at optimum tire chip-sand and tire shred (50 to 100 mm in size)-sand mixing ratios.