Authors: Sjöberg, J; Perman, F; Lope Álvarez, D; Stöckel, B-M; Mäkitaavola, K; Storvall, E; Lavoie, T
Editors: Wesseloo, J
Conference: Eighth International Conference on Deep and High Stress Mining, 28-30 March, Perth
Published: Australian Centre for Geomechanics, Proceedings of the Eighth International Conference on Deep and High Stress Mining, pp.357-372, Perth
With increasing mining depths and excavation volumes comes not only increased rock stresses and more difficult underground mining conditions, but also increased surface effects, in particular from cave mining. The surface effects of deep sublevel cave mining are not well understood and are further explored in this paper, through a case study of the LKAB Kiirunavaara Mine. Two different numerical modelling approaches were used to quantify potential surface effects. The first approach was applied to Sjömalmen (Lake Orebody). This is a non-daylighting portion in the northern end of the mineralisation, above which surface cratering has developed. Three-dimensional (3D) numerical modelling, using the Itasca caving algorithm, was applied to study future mining of Sjömalmen down to Level 1365 m. In the second approach, 2D modelling of the main portion of the Kiirunavaara orebody was conducted, using a caving simulation scheme initially developed at the Luleå University of Technology. This model enabled simulating caving to large depths, in this particular case down to Level 1800 m, for prediction on hangingwall deformations. The actual caving is simulated implicitly in these continuum models. Observational data on cave development and surface cratering, as well as measured ground surface deformations, were used to calibrate the numerical models. For both approaches, deeper mining was shown to significantly affect the ground surface. Ground deformations are not arrested by bulking and/or increased confinement as mining goes deeper. Both modelling approaches have distinct pros and cons. The 2D approach is only applicable to the main portion of the orebody, where 2D geometrical conditions can be reasonably assumed, but calculation times are faster compared to the 3D approach. The models were fairly sensitive to the geomechanical properties and choice of constitutive model. This facilitated calibration, but also implies that an improved characterisation of the rock mass in the cap rock and hangingwall is important for increased reliability in predictive analyses.
Keywords: deep mass mining, ground deformations, numerical modelling, prediction
Sjöberg, J, Perman, F, Lope Álvarez, D, Stöckel, B-M, Mäkitaavola, K, Storvall, E & Lavoie, T 2017, 'Deep sublevel cave mining and surface influence', in J Wesseloo (ed.), Proceedings of the Eighth International Conference on Deep and High Stress Mining
, Australian Centre for Geomechanics, Perth, pp. 357-372.
Duplancic, P & Brady, BHG 1999, ‘Characterisation of caving mechanisms by analysis of seismicity and rock stress’, in G Vouille & P Bérest (eds), Proceedings of the 9th ISRM Congress on Rock Mechanics, vol. 2, Balkema, Rotterdam, pp. 1149–1053.
Hoek, E, Carranza-Torres, C & Corkum, B 2002, ‘Hoek-Brown Failure Criterion - 2002 Edition’, in R Hammah (ed.), Proceedings NARMS-TAC 2002: Mining and Tunnelling Innovation and Opportunity, vol. 1, University of Toronto Press, pp. 267(273.
Hoek, E & Diederichs, MS 2006, ‘Empirical estimation of rock mass modulus’, International Journal of Rock Mechanics and Mining Sciences, vol. 43, pp. 203–215.
Itasca 2013, FLAC3D, software, version 5.01, Itasca Consulting Group, Inc., Minneapolis.
Itasca 2016a, FLAC, software, version 8.0, Itasca Consulting Group, Inc., Minneapolis.
Itasca 2016b, 3DEC, software, version 5.2, Itasca Consulting Group, Inc., Minneapolis.
Lorig, L 2000, The Role of Numerical Modelling in Assessing Caveability, Itasca Consulting Group, Inc., report to the International Caving Study, ICG00-099-3-16.
Mäkitaavola, K, Stöckel, B-M, Sjöberg, J, Hobbs, S, Ekman, J, Henschel, M & Wickramanayake, A 2016, ‘Application of InSAR for Mmonitoring deformations at the Kiirunavaara Mine’, Proceedings of the 3rd International Symposium on Mine Safety, Science and Engineering (ISMS 2016), McGill University, Montreal.
Pappas, DM & Mark, C 1993, Behavior of simulated longwall gob material, report of investigations 9458 USBM.
Pierce, M 2010, A Model for Gravity Flow of Fragmented Rock in Block Caving Mines, PhD thesis, University of Queensland.
Pierce, M 2013, 'Numerical modeling of rock mass weakening, bulking and softening associated with cave mining', ARMA eNewsletter Spring 2013, no. 9, www.armarocks.org
Sainsbury, BL 2012, A model for cave propagation and subsidence assessment in jointed rock masses, PhD thesis, The University of New South Wales, Kensington, New South Wales.
Sainsbury, DP, Sainsbury, B & Lorig, LJ 2010, ‘Investigation of caving induced subsidence at the abandoned Grace Mine’, in Y Potvin (ed.), Proceedings of the Second International Symposium on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, Western Australia, pp. 189–204.
Sainsbury, BL, Sainsbury, DP & Pierce, ME 2011a, ‘A historical review of the development of numerical cave propagation simulations’, in DP Sainsbury, RD Hart, CJ Detournary & MJ Nelson (eds), Proceedings of the 2nd International FLAC/DEM Symposium - Continuum and Distinct Element Numerical Modeling in Geomechanics, Itasca International Inc., Minneapolis, pp. 23–36.
Sainsbury, DP, Sainsbury, BL, Board, MP & Lorig, LJ 2011b, ‘Numerical back-analysis of structurally controlled cave initiation and propagation at the Henderson Mine’, in AT Innacchione, GS Esterhuizen & AN Tutuncu, Proceedings of the 45th US Rock Mechanics/Geomechanics Symposium, American Rock Mechanics Association, Alexandria, Virginia.
Sainsbury, BL & Stöckel, B-M 2012, ‘Historical assessment of caving induced subsidence at the Kiirunavaara Lake orebody’, Proceedings of the 6th International Conference and Exhibition on Mass Mining, Canadian Institute of Mining, Metallurgy and Petroleum, Westmount, Quebec.
Sandström, D 2003, Analysis of the Virgin State of Stress at the Kiirunavaara Mine, Licentiate thesis, Luleå University of Technology, Luleå.
Sjöberg, J, Perman, F, Quinteiro, C, Malmgren, L, Dahnér-Lindkvist, C & Boskovic, M 2012, ‘Numerical analysis of alternative mining sequences to minimise the potential for fault slip rock bursting’, Mining Technology, vol. 121, no. 4, pp. 226–235.
Stöckel, B-M, Mäkitaavola, K & Sjöberg, J 2013, ‘Hangingwall and footwall stability issues in sublevel caving’, in P Dight (ed.), Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, Western Australia, pp. 1045–1060.
Villegas Barba, TF & Nordlund, E 2013, ‘Numerical analyses of the hangingwall failure due to sublevel caving: study case’, International Journal of Mining and Mineral Engineering, vol. 4, no. 3, pp. 201–223.