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UBC Theses and Dissertations

Mechanical response of highly gap-graded mixtures of waste rock and tailings (paste rock) Khalili, Ali


The mixing of mine tailings and waste rock to form “paste rock” prior to disposal is now receiving significant attention from the point of view of sustainable mine waste management practice. This approach has been viewed as a favourable alternative to traditional methods of mine waste disposal because paste rock has the potential to overcome deficiencies, such as acid rock drainage and mechanical instability, associated with traditional methods of mine waste disposal. In consideration of the current limited understanding of the fundamental mechanical response, a systematic laboratory triaxial testing research program was undertaken on paste rock specimens prepared such that the tailings would “just fill” the void spaces between the coarse-particle skeleton. A new “slurry displacement” method was developed for reconstitution of saturated, uniform/homogeneous specimens of highly gap-graded paste rock for triaxial testing. Undrained cyclic triaxial tests indicated that reconstituted paste rock displayed “cyclic-mobility-type” strain development. Strain-softening accompanied by loss of shear strength did not manifest regardless of the applied cyclic stress ratio (CSR). The results suggest that the material is not likely to experience flow deformation under monotonic (static) and/or cyclic loading conditions at least up to the tested initial effective confining stress conditions of up to ≤400 kPa. The behaviour of paste rock was noted to be more similar to the behaviour of rock-only material than that of tailings-only material indicating that the rock skeleton mostly controls the shear resistance in “just filled” paste rock. This finding is in accord with the behaviour of paste rock observed from one-dimensional consolidation tests. In relative terms, paste rock has a higher potential for strain development under a given cyclic stress ratio and number of load cycles in comparison to tailings-only and rock-only materials. The presence of tailings in the pore space between the rock particles appears to decrease the ability of the rock particles to engage contact and develop inter-particle stresses in comparison to the case with rock-only material.

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