Experimental study of the use of mixtures of sand and tire shreds as a geotechnical material

Given the large number of waste tires that are generated every year throughout the world, there is a pressing need of finding innovative and beneficial ways of using scrap tires in the construction of various geotechnical structures. One example of such geotechnical application is the use of tire shreds mixed with sand as a backfill material for mechanically stabilized earth (MSE) walls. Estimation of the resistance to pullout of reinforcement embedded in tire shred-sand mixtures and of the shear strength properties of tire shred-sand mixtures is essential for the design of retaining structures backfilled with tire shred-sand mixtures. Due to the large size of tire shreds used in construction, use of the conventional, small-scale equipment used for testing soils is not possible. In this thesis, we report the results of large-scale laboratory pullout tests performed to study the interaction of two types of reinforcement – geogrid and ribbed metal strip – embedded in tire shred-sand mixtures prepared with various tire shred sizes (9.5mm in nominal size, 50-to-100mm in length, and 100-to-200mm in length) and tire shred-to-sand mixing ratios (tire shred contents of 0%, 12%, 25%, 100% by weight). A large-scale direct shear box was used to evaluate the shear strength properties of tire shred-sand mixtures prepared with large-size tire shreds. In addition, the in situ compaction and load-deformation characteristics of tire shred-sand mixtures were assessed based on tests performed in the context of construction of small-scale demonstration embankments in the field. The pullout capacity of a geogrid/ribbed-metal-strip reinforcement embedded in tire shred-sand mixtures was significantly higher than that of the same reinforcement embedded in tire shreds only. The size of tire shred was found to have a negligible effect on the pullout capacity of the geogrid/ribbed-metal-strip reinforcement embedded in mixtures prepared with either low (12% by weight) or high (100% by weight) tire shreds content. However, for mixtures prepared with 25% tire shreds content (by weight), the geogrid showed a higher pullout capacity when embedded in mixtures prepared using smaller-size tire chips (9.5mm in nominal size) than that when embedded in mixtures prepared with larger-size tire shreds (50-to-100mm and 100-to-200mm in length); this is mainly due to the crossing of the geogrid by the smaller-size tire chips and the higher sand-matrix unit weight achieved in the case of mixtures prepared using tire chips. Based on the large-scale direct shear tests, c-&phis; fitting parameters of 17.5 kPa and 28°, and 0 kPa and 31° were obtained for mixtures prepared at the optimum mixing ratio (tire shreds/sand=25/75, by weight) for tire shred sizes of 50-to-100mm in length and 9.5 mm in nominal size, respectively