Authors: Hall, A; Simser, B; Cai, M

Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2465_80

Cite As:
Hall, A, Simser, B & Cai, M 2024, 'Preconditioning blasting for a deep blind sink shaft excavation ', in P Andrieux & D Cumming-Potvin (eds), Deep Mining 2024: Proceedings of the 10th International Conference on Deep and High Stress Mining, pp. 1221-1236, https://doi.org/10.36487/ACG_repo/2465_80

Download citation as:   ris   bibtex   endnote   text   Zotero


Abstract:
In 2024, Glencore successfully completed an internal winze from 1,150–2,635 m below the surface at Craig Mine in Sudbury, Ontario, Canada. The shaft was sunk in brittle hard rock, which at the depths of construction resulted in seismicity, stress fracturing, pervasive spalling, and rockbursting conditions. The high-horizontal in situ stress meant adverse conditions manifested both in the shaft walls and the bench face. For comparison, a typical lateral development round throws muck away from the face, leaving it partially unconfined and this allows for stress redistribution to occur immediately after the blast. On the other hand, blasted muck from a shaft blast will fill the void created, which confines the bench and inhibits large-scale stress fracturing from occurring. As confinement is reduced from mucking out the round, there is an increase in strainburst risk when operators are required to mark bootlegs and prepare for drilling/loading the next advance. Due to the limited working area associated with a shaft sinking operation, development is highly dependent on physical labour and handheld mining equipment. Compared with lateral mechanised development, fewer tactical controls can be used while shaft sinking to mitigate the risk of rockburst to operators. Preconditioning blasting became a critical control for managing high stress conditions in the shaft sink. There are limited guidelines in published literature for preconditioning blasting in shaft sinking operations and less evidence that preconditioning is providing a benefit. A customised preconditioning blasting strategy was developed based on visual inspections, seismic monitoring, and numerical modelling. The number of holes and location of the ‘de-stress’ charges were adjusted according to the rock mass conditions. It was also essential to institute controls on the shaft bottom mucking to prevent mucking beyond the planned break, so that the stress-fractured material that confined the highly-stressed rock ahead of the bench face was not removed. The experience learned from this project should be beneficial to other future shaft sinking projects at depth.

Keywords: preconditioning blasting, de-stress blasting, strainburst, deep mining, shaft sinking, winze

References:
Andrews, P & Sengani, F 2017, ‘Ameliorating the strain burst risk in a deep level gold mine’, Reutech Mining Newsletter.
Andrieux, P 2005, Application of Rock Engineering Systems to Large-Scale Confined Destress Blasts in Underground Mine Pillars, PhD thesis, Université Laval, Quebec City.
Blake, W & Hedley, DGF 2003, Rockbursts: Case Studies from North American Hard-rock Mines, Society for Mining, Metallurgy, and Exploration, Littleton.
Brown, ET & Hoek, E 1980, Underground Excavations in Rock, CRC Press, Boca Raton.
Cullen, M 1988, Studies of Destress Blasting at Campbell Red Lake Mine, PhD thesis, McGill University, Montreal.
Dickout, MH 1962, ‘Ground control at Creighton mine of the International Nickel Company of Canada Limited’, Proceedings of the 1st Canadian Rock Mechanics Symposium, McGill University, Montreal.
Hall, A, Cai, M, Simser, B & Lindsay, J 2024 ‘Notch formation in vertical excavations in a deep hard rock mine and rock stabilization methodologies’, Deep Resources Engineering, vol. 1, no. 100003,
Hall, A, Simser, B & Cai, M 2021, ‘Mechanisms of deterioration in a bored raise in brittle rock’, International Journal of Rock Mechanics and Mining Sciences, vol. 139, no. 104666.
Mendecki, AJ, Van Aswegen, G & Mountfort, P 1999, ‘A guide to routine seismic monitoring in mines’, in AJ Jager & JA Ryder (eds), A Handbook on Rock Engineering Practice for Tabular Hard Rock, Creda Communications, Cape Town.
Miao, S, Konicek, P, Pan, P & Mitri, HS 2022, ‘Numerical modelling of destress blasting – a state-of-the-art review’, Journal of Sustainable Mining, vol. 4, no. 4, pp. 278–297.
Redpath, JS 1972, ‘Creighton No. 9 shaft, 7137 feet sunk in one lift’, North American Rapid Excavation & Tunnelling Confrence Proceedings, Society of Mining Engineers of the American Institute of Mining, Metallurgical, and Petroleum Engineers, Chicago.
Roux, HG, Leeman, AJA & Denkhaus, ER 1958, ‘De-stressing: A means of ameliorating rockburst conditions: Part I : The concept of destressing and the results obtained from its application, by Roux, Leeman and Denkhaus, published in the Journal, October, 1957: Author’s reply to discussion’, Journal of the Southern African Institute of Mining and Metallurgy, vol. 59, pp. 66–68.
Scoble, MJ, Cullen, M & Makuch, A 1987, ‘Experimental studies of factors relating to destress blasting’, The 28th U.S. Symposium on Rock Mechanics (USRMS), American Rock Mechanics Association, Alexandria.
Sengani, F & Zvarivadza, T 2019, ‘A reconsideration of preconditioning practices in rockburst prone ground conditions in South Africa’. Proceedings of the 26th international mining Congress and Exhibition of Turkey, Baski, Ankara.
Toper, A 2000, ‘The mechanism, optimization and effects of preconditioning’, Journal of the Southern African Institute of Mining and Metallurgy, vol. 100, no. 1, pp. 7–15.
Toper, AZ 2003, The Effect of Blasting on the Rockmass for Designing the Most Effective Preconditioning Blasts in Deep-Level Gold Mines, PhD thesis, The University of the Witwatersrand, Johannesburg.
Vallejos, JA 2022, ‘Rock mechanics and rock engineering for sustainable high stress underground mining’, RaSiM10 - Rockbursts and Seismicity in Mines, Society for Mining, Metallurgy & Exploration, Englewood.




© Copyright 2024, Australian Centre for Geomechanics (ACG), The University of Western Australia. All rights reserved.
View copyright/legal information
Please direct any queries or error reports to repository-acg@uwa.edu.au