Flowslide of tailings dam: understanding the mechanics of intermediate soils for biomediated tailings improvement

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Natural resource extraction is essential to the Canadian economy; Canada has the second largest number of tailings dams worldwide. However, mining activities continue to pose risks to operational and public safety and the environment. A staggering ~275 million m3 of tailings have been released due to tailings dam failures, resulting in >3,000 fatalities. Yet the increased demands for resource extraction will lead to an estimated 10 billion m3/year of additional tailings requiring storage. Current field monitoring programs for tailings dams are insufficient for providing critical forecasts for the development of flow liquefaction (i.e., solid materials behave like fluid under monotonic load) of tailings; the deformation process and the triggering mechanism are not well understood. These knowledge gaps will lead to more dam failures. A greater fundamental understanding of tailings behaviour is vital for Canada's mining sector, economy and environment. The proposed research integrates the mechanics of tailings (as a type of intermediate soil), the deformation of tailings dams, and bio-mediation methods to improve the understanding and mitigation of flowslides in tailings. It is anticipated that 3 PhD students will be trained in state-of-the-art lab and numerical techniques to attain the following research objectives: Objective 1 i) use a data optimization framework for a meta-analysis to assess the effects of fines content on tailings and other intermediate soils. It is to quantify the effects of grain size composition to identify applicable ranges of parameters to be adopted to predict tailings behaviours. Objective 1 ii) is to design and use motion sensors to investigate soil structure collapse during the onset of flow liquefaction; the amplitude of vertical acceleration can reveal particle collision if actual structure collapse occurs. Objective 2 is to simulate the deformation processes of tailings dams using centrifuge modelling. Changes of slope geometry under the influence of a propagating phreatic surface are analyzed, which are expected to reveal the pre-failure geometry change of the tailings dam and the resultant flow constriction, which can induce a drainage condition transition that triggers flow liquefaction. Objective 3 is to study the effects of microbial-induced calcite precipitation treatment on the mechanical behaviours of tailings, focusing on the changes in the microstructure and permeability anisotropy in light of laboratory tests and numerical modelling. The results will provide the fundamental understanding of the bio-mediated soils that are critically needed to fully evaluate its applicability to tailings reclamation. The proposed research program will develop the first-of-its-kind data repository, which will improve our understanding of the development of flow liquefaction in tailings materials as well as the mechanics of intermediate soils, and thus improve the current practices of tailings management.