Abstract:

Backfilling with cemented paste or cemented hydraulic fill requires confinement structures to contain initially fluid backfill within stopes. Significant resources have been invested across the industry to ensure safe and efficient backfilling. Adequate barricade design is essential, ideally coupled with the use of barricade pressure measurements to verify safe loading limits are maintained. Barricade failures are very rare but can constitute high energy events posing significant danger to personnel, mine infrastructure and equipment. As such, the focus upon safe backfilling by managing pressures acting upon containment barricades is highly justified.

The willingness of mines to share “lessons learned” has provided considerable benefit in raising industry-wide safety standards relating to backfilling. For instance, significant case studies presented by Grice (1998), Revel and Sainsbury (2007), and Guresci and Yumlu (2007) have proven extremely valuable in communicating risks and enabling best practices to be adopted. In the decade(s) since these papers were published, we are aware of five barricade failures that have resulted in significant or potentially significant releases of fluid backfill. It is notable that four of these failures resulted from “tight-filling”; emphasizing a clear need to raise awareness of lessons learned and best practices specific to this stage of backfilling a stope.

This paper presents new case study data documenting the cause of these unpublished barricade failures. Tight-fill failures result from pressures increasing at barricades when stopes are overfilled. In some cases, failures are attributed to simple lack of observation that breather pipes that otherwise enable air-escape from the stope are blocked or poorly designed. We demonstrate also that frequently the barricade failures have been enabled by systemic weaknesses such as inadequate barricade design or siting, or issues with construction QA/QC. The final case study emphasizes that even under non-tight filling conditions, attention to QA/QC is essential during backfilling, and barricade pressure measurements should not represent the only control to ensure safe backfilling.

Shotcrete arch barricades represent an increasingly standardized design approach that is widely used across The Industry. This paper aims to highlight risks and best practice approaches so that collectively, operations and design engineers can continue to focus on prioritizing safe backfilling.

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Ben Thompson