Failure Mode
Rationale for the selection of failure mode Based on this, piping failure is further considered in the assessment as credible under a fair-weather condition. There are several failure mechanisms that could lead to slope instability or foundation failure, such as seismicity, liner failure leading to saturation of the embankment, reduction in strength of material, poor construction, and changes in geometry (e.g. unauthorised embankment modifications). Slope instability failure was not considered in this assessment due to the low likelihood of failure based on the design profile, and because the failure scenarios described above are expected to have similar or worse consequences than failure due to slope instability.
Slope instability/foundation failure
5.3.2 Consequence Category Assessment A CCA was prepared for Upper Mundic Gully TSF in accordance with the criteria outlined in ANCOLD and DETSI. An overview of the methods is provided in full in Appendix C and summarised below. ANCOLD Guidelines According to the ANCOLD guidelines, the following two consequence categories need to be assessed as part of a TSF design, considering the risk to human life and severity of damage and loss estimates: 1 - Dam Failure Consequence Category: consequence assessed against the impacts of a catastrophic release of water and tailings following an embankment breach. 2 - Environmental Spill Consequence Category: assessment considering the effects of spilling of water from the dam during a flood or extreme wet period. Risk to human life is expressed either as Population at Risk (PAR) or Potential Loss of Life (PLL): ∕ 5.3.2.1 PAR: Number of buildings or other places of occupation within the failure impact zone, or people working or travelling through a potential impacted zone. Occupancy rate of the impacted areas, duration, and frequency, considering itinerant and non-itinerant populations are used to calculate the PAR; and ∕ PLL: Based on PAR and expected fatality rates, which are based on a combination of flow depth and flow velocity. The severity of loss and damage has been estimated using the maximum flood inundation and severity. The overall severity is determined based on four categories: ∕ Total infrastructure cost; ∕ Impact on owner’s business; ∕ Health and social impacts; and ∕ Environmental impacts. DETSI Guidelines The consequence category based on the DETSI Manual has been estimated in terms of the following three failure types: 5.3.2.2
Project number: 25B061
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