Munkhchuluun, M, Elmo, D, Nadolski, S, Moss, A & Klein, B 2018, 'Presence of natural fracture as an indicator of operational
difficulty for cave operations', in Y Potvin & J Jakubec (eds), Proceedings of the Fourth International Symposium on Block and Sublevel Caving
, Australian Centre for Geomechanics, Perth, pp. 261-270.
Cave mining methods are becoming the methods of choice due to their potential to extract ore from large low-grade deposits at depth at production rates comparable to open pit mines. However, the high upfront capital related to the degree of development and time lag before production require detailed planning and reliable studies to cope with the associated risks. One important geotechnical issue is managing rock mass fragmentation that affects both project value and safety.
Both the scale of the problem and the lack of direct access to the rock mass at project evaluation and design stages make characterisation and accurate prediction of rock mass fragmentation a very difficult task. In this context, caving geomechanics is still largely an empirically based exercise. The discrete fracture network (DFN) approach uses fracture data collected from mapping of boreholes and rock exposures. The DFN approach was used to generate an in situ fragmentation model for the New Afton B1 Cave. The volumetric fracture intensity value (P32) is used as an indicator of the rock mass’s structural character, and provides a direct link to rock mass fragmentation. Major structures were included in the model and the spatial variability of the fracture intensity was analysed to derive a geostatistical model of rock mass fragmentation. The fragmentation ‘block model’ was then superimposed onto New Afton’s PCBCTM historical draw schedule model in an attempt to report blocks, representing the in situ fragmentation to drawpoint with respect to historical logs of hang-up event frequency, which also can refer back to height of draw (HOD). It was found that the influence of natural fractures diminishes gradually as the HOD increases. This is largely due to comminution in the draw column. The results showed that the model could identify areas of high hang-up events during initial draw prior to the column reaching maturity with respect to fragmentation.
Keywords: caving operation, fragmentation, discrete fracture network, hang-up event, height of draw, piecewise linear interpolation, fracture frequency
Bewick, RP, & Kaiser, PK 2016, ‘Characterisation and classification of veined rocks for rock mass behaviour assessment’, Proceedings of MassMin 2016, The Australasian Institute of Mining and Metallurgy, Melbourne, pp. 825–834.
Bergen, RD, Krutzelmann, H & Rennie, DW 2015, NI43-101: Technical Report on the New Afton Mine, British Columbia, Canada, Roscoe Postle and Associates Inc, Toronto.
Brown, ET 2003, Block Caving Geomechanics, Julius Kruttschnitt Mineral Research Centre, Indooroopilly, pp. 304–309.
Brunton, I, Lett, J, Sharrock, GB, Thornhill, T & Mobilio, B 2016, ‘Full-scale flow marker experiment at the Ridgeway Deeps and Cadia East block cave operations’, Proceedings of MassMin 2016, The Australasian Institute of Mining and Metallurgy, Melbourne, pp. 141–150.
Davies, AGL 2015, ‘Case study: understanding the mechanics behind the rockmass deformation observed in an extraction strike drive at New Gold’s New Afton Mine block cave operation’, Proceedings of the 49th US Rock Mechanics/Geomechanics Symposium, American Rock Mechanics Association, Alexandria.
Dershowitz, WS & Herda, HH 1992, ‘Interpretation of fracture spacing and intensity’, Proceedings of the 33rd US Rock Mechanics Symposium, American Rock Mechanics Association, Alexandria.
Elmo, D, Stead, D & Rogers, S 2015, ‘Guidelines for the quantitative description of discontinuities for use in discrete fracture network engineering’, Proceedings of the 13th ISRM Congress, International Society for Rock Mechanics and Rock Engineering, Lisbon, paper 587.
Elmo, D, Liu, Y & Rogers, S 2014a, ‘Principles of discrete fracture network modelling for geotechnical applications’, Proceedings of the 1st International Conference on Discrete Fracture Networking, Canadian Rock Mechanics Association.
Elmo, D 2014b, MINE485: Cave Mining System, week 6 notes – fragmentation, class handout, Norman B. Keevil Institute of Mining Engineering, University of British Columbia, Vancouver.
Elmo, D, Rogers, S, Stead, D & Eberhardt, E 2014c, ‘A discrete fracture network approach to characterize rock mass fragmentation and implication for geomechanical upscaling’, Transaction of the Institutions of Mining and Metallurgy, vol. 123, no. 3,
Elmo, D, Stead, D & Rogers, S 2008, ‘Quantitative analysis of fractured rock masses using a discrete fracture network approach: characterisation of natural fragmentation and implication for current rock mass classification system’, in H Schunnesson &
E Nordlnd (eds), Proceedings of MassMin 2008, Luleå University of Technology, Luleå, pp. 1023–1032.
Kaiser, PK, Amann, F & Bewick, RP 2015, ‘Overcoming challenges of rock mass characterization for underground construction in deep mines’, Proceedings of the 13th International Congress of Rock Mechanics, International Society for Rock Mechanics and Rock Engineering, Lisbon.
Munkhchuluun, M, Elmo, D, Nadolski, S & Klein, B 2018, ‘A piecewise linear interpolation algorithm to reduce the uncertainty of cumulative fracture intensity plots for discrete fracture network modelling’, Proceedings of the 15th International Conference of the International Association for Computer Methods and Advances in Geomechanics, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan.
Nadolski, S, Munkhchuluun, M, Klein, B, Elmo, D & Hart, C 2017, ‘Cave fragmentation in a cave-to-mill context at the New Afton Mine part I: fragmentation and hang-up frequency prediction’, Mining Technology: Transactions of the Institutions of Mining and Metallurgy, vol. 127, no. 2, pp. 75–83, https://dx.doi.org/10.1080/14749009.2017.1351115
Turichshev, A & Hadjigeorgiou, J 2015, ‘Experimental and numerical investigation into the strength of intact veined rock’, Rock Mechanics and Rock Engineering, vol. 48, no. 5, pp. 1897–1912.
Vyazmensky, A, Elmo, D & Stead, D 2010, ‘Role of rock mass fabric and faulting in the development of block caving induced surface subsidence’, Rock Mechanics and Rock Engineering, vol. 43, no. 5, pp. 533–556, https://dx.doi.org/10.1007/s00603-009-0069-6