Sudden slumping of hydraulic fills inside geotextile bags

9th International Symposium on Mining with Backfill
Abstract Hydraulic fills are widely used in the tabular, steeply dipping stopes of the South African gold and platinum mines as an integrated process within a daily cycle of drill and blast. Therefore only a limited time window exists to fill the geotextile bags used as fill containment, without the risk of loosing production. Consequently, mines tend to increase the flow rate to the stopes, although this compromises adequate drainage, consolidation and strength development during filling.

Recent underground measurements inside the geotextile bag have revealed that at high rates of rise, the backfill can remobilise within a limited area inside the geotextile bag during filling. This sudden downward surge of backfill exerts, for only a few seconds, additional loading onto the geotextile, its supporting mesh and the props. This unstable behaviour poses a serious threat, as it can push props out of place, thereby damaging the geotextile bag and potentially triggering a mud slide down the stope.

To reduce the risk of accidents, the phenomenon of sudden slumping was further investigated for various filling conditions in the laboratory. The results confirmed that the peak pressures associated with the sudden slumping can be more than three times the pressures experienced during steady-state filling.

Based on this new insight, the current best practice for hydraulic backfilling was critically reviewed. A practical approach to implement meaningful standards is presented to ensure safe operations in relation to the consistency of the backfill quality and the appropriate match of geotextile characteristics with backfill properties.
Keywords: Hydraulic Fill, risks of accidents, Geotextile, insitu measurements, backfill quality, laboratory testing, slumping, rate of rise
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