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Tailings Dam Break Analysis Performed for the PFS Study of a Downstream Raised TSF in South America

Tailings and Mine Waste Conference (2023 : Vancouver, B.C.); University of British Columbia. Norman B. Keevil Institute of Mining Engineering

In this case study, a tailing dam breach analysis (TDBA) was conducted during a pre-feasibility (PFS) study of a tailings storage facility (TSF) and its two main tailings dams, proposed to be constructed using the downstream raised method to provide an additional 600 Mm³ of storage capacity. The objective of the TDBA was to assess the potential risks posed by the construction of the tailings dams and identify the mitigation measures and controls that would be required to reduce hazards in subsequent engineering phases. The TSF dams will retain tailings (that are susceptible to liquefaction) and a supernatant pond in the final phase of construction and during operation; therefore, the dams were identified as Case 1A as per CDA (2021). During a dam failure, the total volume of tailings released is the combination of the volume of tailings that will be mobilized/eroded by the free water (defined as Process I in CDA, 2021) and the volume of liquefiable tailings (defined as Process II in CDA, 2021). These volumes are difficult to establish, and currently, there are limitations and uncertainties in methodologies available in the industry to determine these volumes. The breach process is a complex interaction of the fluid hydrodynamics (e.g., erosion and sediment transportation) and the geotechnical characteristics of the dam. This process is not well understood and is currently a topic of research. Furthermore, the volume released during a dam breach is primarily a function of the tailings characteristics and the breach size (e.g., breach invert) that depends on the materials and conditions of the dam and its foundation. In the context of this study, the ultimate downstream area of flood inundation is not dependent on the breach mechanism but rather on the released volume and the released rate (e.g., breach formation time). The failure modes that were adopted for the TDBAs were overtopping during an extreme event (i.e., a rainy day) and internal erosion or earthquake during normal conditions (i.e., a sunny day). These were found to be credible failure modes. Once the failure of a dam is triggered, erodible processes will follow and accelerate as the breach expands, allowing increased flow, resulting in an uncontrolled release of water and tailings. The greatest challenge during the PFS study was predicting the final TSF configuration (in-situ tailings density and beach slopes) and analyzing the potential failure modes and the effects on the resulting breach geometry for downstream-raised tailings dams. This paper outlines the methodology used to assess the above-mentioned parameters that served as an input to the TDBA. In addition, sensitivity analyses were carried out to validate the inputs and their effects on the results, including recommendations for subsequent engineering phases.

Text

2023-12-08

Attribution 4.0 International

http://hdl.handle.net/2429/86848

Unreviewed

http://creativecommons.org/licenses/by/4.0/