Authors: Pakula, A; Preston, R; Kennard, D; MacInnis, C

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Pakula, A, Preston, R, Kennard, D & MacInnis, C 2019, 'Stabilising an underground void: monolithic construction using self-consolidating concrete', in AB Fourie & M Tibbett (eds), Mine Closure 2019: Proceedings of the 13th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 263-274,

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In 2007, during a planned water level raise at the Giant Mine, which had recently been placed into care and maintenance, a large movement of fill occurred in a series of connected vertically stacked cut-and-fill stopes. The movement mobilised over 170,000 metric tonnes of previously placed unconsolidated rock and sand fill and left a 70,000 m3 void separated from arsenic trioxide storage vaults, by a thin sill pillar. Review of historical mine plans and investigations onsite suggested that timber sill mats and bulkheads which had likely destabilised when the area became variably saturated during flooding, created a connection between remnant voids in the upper and lower mining horizons resulting in the void. Furthermore, it was determined that if the water level was changed again, with either a rise or drawdown that the rock and fill within the stope below the void could once again be mobilised, further reducing the stability of the void. The mine is to be remediated and closed and a permanent solution to stabilising this void, which is approximately 85 to 125 m below ground surface, was required. Given the lack of future underground access and a desire by the project proponent to reduce long-term monitoring and care requirements, a unique solution was required. While stabilising mine voids during active production mining or during mine closure activities, practitioners would typically utilise a cemented mine waste product such as cemented rockfill (CRF), cemented paste backfill (CPB) or cemented sand fill. Because of the potential for the previously placed sand and rockfill in the void to move deeper into the mine void and possibly destabilise the workings, a manufactured sill pillar that would stay in place should the material below it move was required. In this case, it was determined that the void span was sufficiently large that these types of materials would not be self-supporting should such a movement occur. Therefore, a self-consolidating concrete (SCC), also known as self-levelling concrete was used to manufacture a 16,600 m3 (70 x 24 x 10 m) monolithic concrete sill pillar to be installed.

Keywords: mine closure, manufactured sill pillar, self-consolidating concrete, self-levelling concrete, arsenic, arsenic trioxide, Giant Mine, Giant Mine Remediation Project, mine backfill, remediation, stope stabilisation

ASTM International 2018, Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens, ASTM C39/C39-18, ASTM International, West Conshohocken.
ASTM International 2016, Standard Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance, ASTM C403/C403M-16, ASTM International, West Conshohocken.
ASTM International 2014a, Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates, ASTM C136/C136M-14, ASTM International, West Conshohocken.
ASTM International 2014b, Standard Test Method for Slump Flow of Self-Consolidating Concrete, ASTM C1611/C1611M-14, ASTM International, West Conshohocken.
ASTM International 1998, Standard Test Method for Expansion and Bleeding of Freshly Mixed Grouts for Preplaced-Aggregate Concrete in the Laboratory, ASTM C940, ASTM International, West Conshohocken.
Crown and Indigenous Relations and Northern Affairs Canada & Government of the Northwest Territories 2019, Closure and Reclamation Plan for Giant Mine, prepared for the Mackenzie Valley Land and Water Board, Yellowknife.
Google n.d., Giant Mine,
Rocscience n.d., RS2, computer software, Toronto,
Silke, R 2009, The Operational History of Mines in the Northwest Territories, Canada, viewed 8 April 2019,

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