Authors: Grabinsky, MW; Thompson, BD; Veenstra, RL

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Grabinsky, MW, Thompson, BD & Veenstra, RL 2023, 'Cemented paste backfill strength profiles for continuous pouring and liquefaction resistance', in GW Wilson, NA Beier, DC Sego, AB Fourie & D Reid (eds), Paste 2023: 25th International Conference on Paste, Thickened and Filtered Tailings, University of Alberta, Edmonton, and Australian Centre for Geomechanics, Perth, pp. 257-270,

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Current practice for backfilling tall stopes (e.g., long hole or Alimak) with cemented paste backfill (CPB) involves an initial plug pour to protect the barricade, followed by a main pour for the remaining stope. Many mines use higher binder content in the plug to accelerate curing time, supporting continuous pouring (i.e., no plug cure time before starting the main pour). An analytical solution to assess the required plug strength for continuous pours was recently proposed in a paper by Grabinsky et al. (2021). Similarly, various heuristics have been published suggesting a minimum Unconfined Compressive Strength will be sufficient to prevent CPB liquefaction under even the most implausible extreme loading events. However, practising mining engineers would benefit from a more straightforward design approach to assess the suitability of their backfill’s evolving strength in continuous pour and liquefaction resistance design issues. To this end, the authors have found it useful to consider the concept of a Strength Profile with depth in the plug, recognising that this Strength Profile is transient (i.e., changing with time) and must be considered for different critical stages of the plug pour and main pour. The Strength Profile design concept is explained in this paper and demonstrated using key case histories from mines where the backfill was previously monitored during continuous pouring and where the backfill materials were extensively characterised in the laboratory.

Keywords: cemented paste backfill, continuous filling, plug stability analysis, liquefaction resistance

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