Moser, A, Wagner, H & Schinagl, S 2017, 'Application of rock mass classification systems as a tool for rock mass strength determination', in J Wesseloo (ed.), Deep Mining 2017: Proceedings of the Eighth International Conference on Deep and High Stress Mining
, Australian Centre for Geomechanics, Perth, pp. 569-585, https://doi.org/10.36487/ACG_rep/1704_38_Moser
The determination of the in situ rock mass strength can be found among the most difficult and challenging investigations in underground mining. The focus of a research project carried out in an underground magnesite mine was the assessment of the rock mass strength using the conventional approaches of rock mass classification, namely Rock Quality Designation (RQD) value after Deere and Deere (1988), Geological Strength Index (GSI) after Hoek et al. (2002), Rock Mass Rating (RMR) after Bieniawski (1989), Q-system after Barton (1990) and Mining Rock Mass Rating (MRMR) after Laubscher (1990) and information on laboratory rock strength. These methods were applied in an underground drift in the vicinity of a stoping panel in order to determine the rock mass strength as well as the influence of the approaching mining activities on the rock mass conditions. Supplementary, core drilling was conducted to provide samples for rock strength determination as well as for the observation of the rock mass conditions using a borehole camera. Based on the results of the rock mass classification systems and uniaxial rock strength tests, the rock mass strength was determined using different approaches. Further on the rock mass strength results were compared to the estimated in situ state of stress, calculated by the weight of the overlying rock strata, assuming a hydrostatic state of stress and physical conditions of the drift. The results from the rock mass strength determination were in the range of 15–450% of the estimated in situ pre-mining state of stress. The results of borehole observations and RQD measurements show considerable variations in rock conditions in the immediate vicinity of drift ranging from extensive fracturing to fairly competent rock. However, with further distance from the drift, the condition of the rock mass changes to that of a massive and undisturbed rock mass.
This highlights the difficulties of arriving at realistic rock mass strength values for the deep section of the magnesite mine. The aspects concerning this problem are discussed in detail.
Keywords: rock fracturing, rock mass classification, rock mass strength, deep mining
Barton N 1990, ‘Scale effects or sampling bias?’, in A Pinto da Cunha (ed.), Proceedings of the First International Workshop on Scale Effects in Rock Masses, 7–8 June, Loen, Balkema, Rotterdam, pp. 31–59.
Barton, N 2002, ‘Some new Q-value correlations to assist in site characterisation and tunnel design’, International Journal of Rock Mechanics and Mining Sciences, vol. 39, no. 2, pp. 185–216.
Bieniawski, ZT 1989, Engineering Rock Mass Classifications, John Wiley & Sons, New York, pp. 251.
Brady, BHG & Brown, ET 2006, Rock Mechanics for Underground Mining, 3rd edn, Springer Science & Business Media, Berlin.
Cai, M, Kaiser, PK, Uno, H, Tasaka, Y & Minami, M 2004, ‘Estimation of rock mass deformation modulus and strength of jointed hard rock masses using the GSI system’, International Journal of Rock Mechanics and Mining Sciences, vol. 41, pp. 3–19.
Deere, DU & Deere, DW 1988, ‘The Rock Quality Designation (RQD) index in practice’, in L Kirkaldie (ed.), Rock Classification Systems for Engineering Purposes, ASTM STP 984, ASTM International, West Conshohocken, pp. 91–101.
Edelbro, C 2003, Rock Mass Strength: A Review, technical report, Luleå University of Technology, Luleå.
Hoek, E, Brown, ET, 1980, ‘Empirical strength criterion for rock masses’, Journal of the Geotechnical Engineering Division, ASCE 106 (GT9), pp. 1013–1035.
Hoek, E, Carranza-Torres, C & Corkum, B 2002, ‘Hoek-Brown failure criterion – 2002 edition’, in R Hammah (ed.), Proceedings of the 5th North American Rock Mechanics Symposium and the 17th Tunnelling Association of Canada Conference, University of Toronto, Toronto, pp. 267–273.
Hoek, E, Carter, TG & Diederichs, MS 2013, ‘Quantification of the Geological Strength Index Chart’, in LJ Pyrak-Nolte, A Chan, W Dershowitz, J Morris & J Rostami (eds), Proceedings of the 47th US Rock Mechanics/Geomechanics Symposium, 23–26 June 2013, San Francisco, American Rock Mechanics Association, Alexandria, pp. 1757–1764.
Kaiser, PK & Kim, B-H 2015, ‘Characterization of strength of intact brittle rock considering confinement-dependent failure processes’, Rock Mechanics and Rock Engineering, vol. 48, pp. 107–119.
Laubscher, DH 1990, ‘A geomechanics classification system for the rating of rock mass in mine design’, The Journal of the South African Institute of Mining and Metallurgy, vol. 90, no. 10, pp. 257–273.
Martin, CD, Kaiser, PK & McCreath, DR 1999, ‘Hoek–Brown parameters for predicting the depth of brittle failure around tunnels’, Canadian Geotechnical Journal, vol. 36, pp. 136–151.
Marinos, P & Hoek, E 2000, ‘GSI – A geologically friendly tool for rock mass strength estimation’, Proceedings of the GeoEng 2000 Conference, Melbourne, Technomic Publishers Co Inc, Lancaster, pp. 1422–1442.
Ramamurthy, T 1985, ‘Stability of rock mass’, Indian Geotechnical Journal, vol. 16, no. 1, pp. 1–75.
Salamon, MDG & Munro, AH 1967, ‘A study of the strength of coal pillars’, The Journal of the South African Institute of Mining and Metallurgy,vol. 68, no. 2, pp. 55–67.
Siefert, M 2009, ‘Verfahren zur qualitativen und quantitativen Beschreibung des Gebirges, 2 Teil: Quantitative Gebirgsbeschreibung‘, BHM Berg- und Hüttenmännische Monatshefte, vol. 154, no. 10, pp. 426–440.
Trueman, R 1988, An evaluation of strata support techniques in dual life gateroads, PhD thesis, Cardiff University, Cardiff.
Wiseman, N 1979, Factors affecting the design and condition of mine tunnels, Research Report No. 45/79, Chamber of Mines of South Africa, Pretoria, South Africa, pp. 22.
Zhang, L 2010, ‘Estimating the Strength of Jointed Rock Masses’, Rock Mechanics and Rock Engineering, vol. 43, pp. 391–402.
Zhang, L 2016, ‘Determination and applications of rock quality designation (RQD)’, Journal of Rock Mechanics and Geotechnical Engineering, vol. 8, pp. 389–397.