Modelling the Response of Evolutive Granular Media to Blast Loadings: Cemented Tailings Backfill

Abstract

Cemented tailings backfill (CTB), an evolutive granular medium, is utilized extensively in underground mines as a sustainable solution to tailings disposal and for ground control. To achieve full ore recovery, the backfill mass is often exposed to mine blasts during the extraction of ore pillars. Nevertheless, limitations in knowledge regarding the dynamic response of CTB and the lack of design standards to ensure backfill stability during blasting have caused numerous failure incidents of backfill systems. Therefore, the proposition to utilize reliable tools for a rational characterization of CTB behaviour under mine blasts has become imperative. However, current studies conducted to evaluate blast response of mine backfills are based on empirical equations and simple constitutive models, and the evolutive nature of CTB due to multiphysics processes occurring in the material has not yet been considered. Therefore, in this PhD study, a series of fundamental multiphysics models are developed to assess the blast response of CTB with ongoing cementation. Specifically, a novel coupled chemo-viscoplastic cap model is developed to characterize the rate-dependence, irrecoverable compaction, and nonlinear hydrostatic behaviour of CTB under blast loading. The evolution in the dynamic response of CTB due to binder hydration is incorporated in the model and quantified with a binder hydration model. Moreover, the performance of CTB is not only affected by the hydration of binders (chemical, C), but is also significantly influenced by the thermal (T), hydraulic (H), and mechanical (M) factors it is subjected to during its service life. Therefore, a new multiphysics-viscoplastic cap model is then developed to characterize the blast response of CTB under the impact of complex THMC processes of its curing stage. Furthermore, as a granular medium, the early-age CTB with no or negligible cementation is also subjected to the risk of blast-induced liquefaction. Thus, a new total-stress viscoplastic cap model is developed to account for the impedance of pore water and capture excess pore pressure development in early-age backfills during blast loading. The developed multiphysics models are validated against a series of experiments on both laboratory and field scales, and the effectiveness and predictive ability of the models are verified by good agreement between the simulated and measured results. Then, the validated models are applied to practical engineering issues pertaining to field backfilling operations. These include simulation of the blast wave propagation in field CTB structures and the blast-induced liquefaction susceptibility of early-age fill mass, as well as blast-induced stress redistribution in early-age fill mass. The different dynamic responses of CTB to varied backfilling conditions and design strategies are then scrutinized and analyzed. Thus, the research performed in this PhD study can provide useful tools and technical insight for a better understanding of the blast response of CTB as well as optimal design of CTB systems in such dynamic condition.