Bewick, RP, Ouellet, A, Otto, S & Gaudreau, D 2017, 'Importance of understanding laboratory strength and modulus testing data for deep mining in hard brittle rocks', in J Wesseloo (ed.), Proceedings of the Eighth International Conference on Deep and High Stress Mining
, Australian Centre for Geomechanics, Perth, pp. 827-842, https://doi.org/10.36487/ACG_rep/1704_57_Bewick
One common aspect of deep mining is the massive rock mass conditions leading to a failure process where new fractures are created through the rock. Therefore, the three dominate rock mass characteristics required for deep mining deposits are the strength, elastic properties, and pre-mining stress state. This paper focuses on characterising the strength parameters and elastic properties of rocks for deep mining purposes. Too often, strength testing data does not receive proper attention. Details are provided on the specification of confining pressures for both low (excavation skin) and high (squat pillars) confinement design specific challenges, the filtering of data to assess Hoek–Brown intact rock strength envelopes, and the interpretation of testing results.
Laboratory testing data from a deep mining deposit is presented to show appropriate filtering for the determination of strength by failure type. Next the importance of understanding the elastic properties is discussed and it is shown how different relative magnitudes in elastic moduli and lithologic unit geometry impact stress and strain changes between rock units. This understanding assists engineers in determining the modulus differences leading to potential stress but, more importantly, strain gradients in the rock mass that have the potential for the generation of seismicity and rockbursts.
Keywords: material parameters, modulus, compressive strength, brittle rock
Aglawe, J 1999, Unstable and Violent Failure around Underground Openings in Highly Stressed Ground, PhD thesis, Queen's University, Kingston.
Bewick, RP 2013, Shear Rupture of Massive Brittle Rock under Constant Normal Stress and Stiffness Boundary Conditions, PhD thesis, University of Toronto, Toronto.
Bewick, RP & Kaiser, PK 2014, ‘Discussion on “An Empirical Failure Criterion for Intact Rocks” by Peng et al. (2013)’, Rock Mechanics and Rock Engineering, 47: 817.
Bewick, RP, Kaiser, PK & Valley, B 2011, ‘Interpretation of triaxial testing data for estimation of the Hoek-Brown strength parameter mi’, Proceedings of the 45th US Rock Mechanics/Geomechanics Symposium, American Rock Mechanics Association, Alexandria.
Bewick, RP, Amann, F, Kaiser, PK & Martin, CD 2015, ‘Interpretation of UCS test results for engineering design’, Proceedings of the 13th ISRM International Congress of Rock Mechanics, International Society for Rock Mechanics, Lisboa.
Bewick, RP, Valley, B, Runnalls, S, Whitney, J & Krynicki, Y 2009, ‘Global approach to managing deep mining hazards’, in M Diederichs & G Grasselli (eds), Proceedings of the 3rd CANUS Rock Mechanics Symposium, May, Toronto, paper 3994.
Castro, LAM, Grabinbsky, MW & McCreath, DR 1997, ‘Damage imitation through extension fracturing in a moderately jointed brittle rock mass’, Proceedings of the 36th U.S. Rock Mechanics Symposium, 30 June–2 July, New York.
Crouch, S 1974, ‘Analysis of rock bursts in cut and fill stopes’, Journal of Scientific & Industrial Research, vol. 256, pp. 298–303.
Diederichs, MS 1999, Instability of hard rock masses: the role of tensile damage and relaxation, PhD thesis, University of Waterloo, Waterloo.
Diederichs, MS, Carter, T & Martin, DC 2010, ‘Practical rock spalling prediction in tunnels’, World Tunneling Congress, Vancouver.
Escartin, J, Hirth, G & Evans, B 1997, ‘Nondilatant brittle deformation of serpentinites: Implications for Mohr-Coulomb theory and the strength of faults’, Journal of Geophysical Research, vol. 102, pp. 2897–2913.
Golder 2015, Laboratory testing completed for a veined limestone, Golder Associates Ltd.
Golder 2016, Laboratory testing completed at Golder’s Rock Testing Laboratory for a Meta-Sedimentary rock unit, Golder Associates Ltd.
Hoek, E 1983, ‘Strength of jointed rock masses’, Geotechnique, vol. 23, no. 3, pp. 187–223.
Hoek, E 1968, ‘Brittle failure of rock’, in KG Stagg & OC Zienkiewicz (eds), Rock Mechanics in Engineering Practice, Wiley, London, pp. 99–124.
Hoek, E & Brown, ET 1980a, Underground excavations in rock, Institution of Mining and Metallurgy, London.
Hoek, E & Brown, ET 1980b, ‘Empirical strength criterion for rock masses’, Journal of Geotechnical and Geoenvironmental Engineering, American Society of Civil Engineers, vol. 106, no. GT9, pp. 1013–1035.
Hoek, E & Brown, ET 1997, ‘Practical estimates of rock mass strength’, International Journal of Rock Mechanics and Mining Sciences, vol. 34, no. 8, pp. 1165–1186.
Hoek, E & Diederichs, MS 2006, ‘Empirical estimation of rock mass modulus’, International Journal of Rock Mechanics and Mining Sciences, vol. 43, pp. 203–215.
Hoek, E, Kaiser, PK & Bawden, WF 1995, Rock support for underground excavations in hard rock, Balkema, pp. 215.
Jaeger, JC & Cook, NGW 1976, Fundamentals of Rock Mechanics, 2nd edn, Chapman and Hall, London.
Kaiser, PK & Kim, B-H 2014, ‘Characterization of strength of intact brittle rock considering confinement-dependent failure processes’, Rock Mechanics Rock Engineering.
Kaiser, PK, Amann, F & Bewick, RP 2015, ‘Overcoming challenges of rock mass characterization for underground construction in deep mines’, Proceedings of the 13th ISRM International Congress of Rock Mechanics, International Society for Rock Mechanics, Lisboa.
Kaiser, PK, Diederichs, MS, Martin, CD, Sharp, J & Steiner, W 2000, ‘Underground works in hard rock tunneling and mining’, Proceedings of the International Conference on Geotechnical and Geological Engineering, vol. 1, invited papers, Melbourne, pp. 841–926.
Maloney, S, Kaiser, PK & Vorauer, A 2006, ‘A re-assessment of in situ stresses in the Canadian Shield’, Proceedings of the 41st US Symposium on Rock Mechanics — 50 years of Rock Mechanics – Landmarks and Future Challenges, Golden, Colorado.
Martin, CD 1993, Strength of massive granite around underground openings, PhD thesis, University of Manitoba, Manitoba.
Mogi, K 1966, ‘Pressure dependence of rock strength and transition from brittle fracture to ductile flow’, Bulletin of the Earthquake Research Institute, vol. 44, pp. 215–232.
Paterson, MS 1958, ‘Experimental deformation and faulting in Wombeyan marble’, Geological Society of America Bulletin, vol. 69, pp. 476–548.
Perras, MA & Diederichs, MS 2014, ‘A review of the tensile strength of rock: concepts and testing’, Geotechnical and Geological Engineering, vol. 32, pp. 525–546.
Salamon, MDG 1970, ‘Stability, instability and design of pillar workings’, International Journal of Rock Mechanics and Mining Sciences, pp. 613–663.
Schofield, A & Wroth, P 1968, Critical State Soil Mechanics, McGraw-Hill, p. 310, ISBN 978-0641940484.
Valley, B 2012, Structural Geology Guidelines for Burst Prone Mines, Ontario.
Velde, B, Moore, D, Badri, A & Ledesert, B 1993, ‘Fractal and length analysis of fractures during brittle to ductile changes’, Journal of Geophysical Research, vol. 98, no. B7, pp. 11935–11940.
Walton, G 2014, Improving continuum models for excavations in rock masses under high stress through an enhanced understanding of post-yield dilatancy, PhD thesis, Queen’s University, Kingston, pp. 602.