Geotechnical risk management for open pit mine closure: a sub-arctic and semi-arid case study
Bibliographic record
Abstract
De Beers is currently developing closure plans for two open pit mines. At first glance they appear quite similar; both are relatively remote, have operated for 10 years, have similar pit dimensions (250–300 m deep and 1.5 km wide) and have Palaeozoic sedimentary host lithologies with weak upper units overlying more competent lower materials. However, Victor Mine in the sub-Arctic Canada, is one of De Beers wettest mines (dewatering volume of 75,000 m3/d) and is hosted predominantly in good quality limestone with excellent final wall performance. While Voorspoed Mine, in semi-arid Southern Africa required virtually no dewatering, has poor wall performance associated many with mudstone and country rock breccia instabilities. Victor Mine is expected to achieve stable pit lake in less than 10 years (and less than 2 years with supplementation from a nearby river), while Voorspoed will take over 100 years to reach ultimate pit lake level (due to low groundwater inflows, high evaporation and limited opportunity for flow supplementation). This paper describes a process to determine closure stability design acceptance criteria (DAC) and characterise the zone of long-term surface disturbance surrounding the pit (i.e.: potentially unstable pit edge zone to define the closure exclusion zone). This involved: These results along with the well documented historical slope performance provided the basis for detailed Geotechnical Risk Assessments which addressed two periods. Risk-based monitoring plans were developed along with Trigger Action Response Plans (TARPs) to ensure that closure of the pit proceeds safely and efficiently while satisfying the regulatory requirements.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".