Consolidated Undrained Shear Behavior of Synthetic Waste Rock and Synthetic Tailings Mixtures

The objective of this study was to evaluate the effects of mixture ratio (R) and synthetic tailings composition (i.e., particle-size distribution) on the undrained shear behavior of mixed synthetic waste rock and tailings (S-WR&T). Crushed gravel was used as a granitic waste rock (GWR), and mixtures of sand, silt, and clay were used to create average synthetic tailings (AST) and fine synthetic tailings (FST). Mixtures of S-WR&T were prepared to simulate coarse-dominated, optimal, and fine-dominated mixtures. Testing was conducted in consolidated undrained triaxial compression at target effective confining stresses of 10, 50, and 100 kPa. Coarse-dominated S-WR&T mixtures exhibited comparable shear behavior to pure GWR. Fine-dominated S-WR&T mixtures exhibited shear behavior that was more similar to pure synthetic tailings. However, an analysis of the undrained shear response indicated that the presence of GWR in fine-dominated S-WR&T mixtures can transition undrained flow behavior of pure synthetic tailings to limited-flow or no-flow behavior that is representative of GWR. The AST mixture prepared at optimal mixing conditions yielded an effective stress friction angle (phi'(t)) = 48 degrees, and fine-dominated mixtures of AST yielded phi'(t) = 44 degrees. The fine-dominated mixtures for FST yielded phi'(t) ranging from 32 degrees to 38 degrees, whereby phi'(t) increased with an increase in the amount of GWR in the mixture.