Large quantities of waste tires can be beneficially used by incorporating them into structural fill employed in earthwork projects such as highway embankments and backfills for retaining structures. These applications require knowledge of the bulk mechanical properties of tire chips and soil-tire chip mixtures. The objective of the study described in this paper was to evaluate the mechanical properties and behavior of waste tire chips and their mixtures with fine- and coarse-grained soils. Large-scale laboratory testing equipment was used to conduct the study. Tests were conducted to evaluate shear strength, deformability, and compressibility. Mixtures made with typical backfill soils such as clean sand, sandy silt, and clay were tested. Results of the tests show that tire chips and soil-tire chip mixtures behave like soils, but are more compressible and also require more deformation to mobilize their ultimate shear strength. Incorporation of tire chips in the backfill results in a reduction in unit weight and, for mixtures containing sand or sandy silt, an increase in shear strength. In contrast, clay-tire chip mixtures have the same or lower shear strength as clay alone. Strength envelopes for sand-tire chip mixtures can be nonlinear, and have virtually no cohesion intercept. Mixtures containing sandy silt behave similar to mixtures made with sand, except the shear strength envelope for the sandy silttire chip mixture is linear and has a cohesion intercept. Sand-tire chip and sandy silt-tire chip mixtures exhibit similar long-term compression behavior.