Authors: Duran, A


Cite As:
Duran, A 2016, 'Rock mass assessment — what goes wrong?', in PM Dight (ed.), APSSIM 2016: Proceedings of the First Asia Pacific Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, pp. 493-506,

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The use of the Geological Strength Index (GSI) to assess rock mass quality in combination with the Hoek–Brown rock mass shear strength criteria has become widely used within the geotechnical fraternity to assess stability for mine pit slopes. Two approaches for the assessment of GSI appear within the literature. Firstly, quantitative approaches as proposed by Cai et al. (2004), Hoek et al. (2013), Russo (2009) and Sonmez and Ulusay (2002). Secondly, a visual approach Marinos and Hoek (2000), Bertuzzi et al. (2016), Pells et al. (2016) and Russo (2009) and with the latter three set of authors indicating comparable assessment by either the visual or quantitative approach. Moreover, recent discussions also present qualifications and applicability of GSI by Carter and Marinos (2014) and Kaiser et al. (2015). Based on the author’s experience the findings of the above studies are discussed. Examples are utilised to highlight aspects of rock mass quality assessment where geotechnical logging of borehole core is often the only source of evaluation. The author presents two case studies where it has been possible to compare the results of the available quantification schemes with back-analysed strengths from large scale pit instability.

Keywords: rock mass assessment

Bertuzzi, R, Douglas, DJ & Mostyn, G 2016, ‘Comparison of quantified and chart GSI for four rock masses’, Engineering Geology, vol. 202, pp. 24–35.
Bieniawski, ZT 1989, Engineering Rock Mass Classification, New York, Wiley Interscience.
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.
Carter, TG & Marinos, V 2014, ‘Use of GSI for rock engineering design’, in Proceedings 1st International Conference on Applied Empirical Design Methods in Mining, Lima, pp. 1–19.
Carter, TG, Diederichs, MS & Carvalho, JL 2008, ‘Application of modified Hoek–Brown transition relationships for assessing strength and post-yield behaviour at both ends of the rock competence scale’, Journal of the Southern African Institute of Mining and Metallurgy, vol. 108, no. 6, pp. 325–338.
Dinc, OS, Sonmez, H, Tunusluoglu, C & Kasapoglu, KE 2011, ‘A new general empirical approach for the prediction of rock mass strengths of soft to hard rock masses’, International Journal of Rock Mechanics and Mining Sciences, vol. 48, pp. 650–665.
Douglas, KJ & Mostyn, G 1999, ‘Strength of large rock masses – field verification, Rock Mechanics for Industry’, in Proceedings of the 37th US Rock Mechanics Symposium, Vale Colorado, Balkema Rotterdam, vol. 1, pp. 271–276.
Duran, A 2015, ‘30 Case Studies: Using borehole data for rock mass quality assessment’, in Proceedings Slope Stability 2015, Cape Town.
Hoek, E 1983, ‘Strength of jointed rock masses’, 23rd Rankine Lecture, Géotechnique, vol. 33, no. 3, pp. 187–223.
Hoek, E & Brown, ET 1980, ‘Empirical strength criterion for rock masses’, Journal of the Geotechnical Engineering Division, vol. 106, pp. 1013–1035.
Hoek, E & Brown, ET 1997, ‘Practical estimates of rock mass strength’, International Journal of Rock Mechanics and Mining Sciences, vol. 34, pp. 1165–1186.
Hoek, E, Carter, TG & Diederichs, MS 2013, ‘Quantification of the Geological Strength Index chart’, in 47th US Rock Mechanics/Geomechanics Symposium, ARMA 13-672, San Francisco.
Hoek, E, Kaiser, PK & Bawden, WF 1995, Support of underground excavations in hard rock, Rotterdam, Balkema.
Hoek, E, Marinos, P & Benissi, M 1998, ‘Applicability of the geological strength index (GSI) classification for very weak and sheared rock masses. The case of the Athens Schist Formation’, Bulletin of Engineering Geology and the Environment, vol. 57, no. 2, pp. 151–160.
Hoek, E, Marinos, P & Marinos, V 2005, ‘Characterisation and engineering properties of tectonically undisturbed but lithologically varied sedimentary rock masses’, International Journal of Rock Mechanics and Mining Sciences, vol. 42, pp. 277–285.
Kaiser, PK, Amann, F & Bewick, BP, 2015, ‘Overcoming challenges of rock mass characterization for underground construction in deep mines’, in The 13th International Congress of Rock Mechanics, Montreal.
Laubscher, DH & Jakubec, J 2000, ‘The IRMR/MRMR rock mass classification system for jointed rock masses’, Society for Mining, Metallurgy, and Exploration, pp. 475–481.
Marinos, PV 2010, ‘New proposed GSI classification charts for weak or for complex rock masses’, in 12th International Congress of Geological Society of Greece, Patras, pp. 1248–1258.
Marinos, P & Hoek, E 2000, ‘GSI: A geologically friendly tool for rock mass strength estimation’, in GeoEng2000: An International Conference on Geotechnical & Geological Engineering, International Society for Rock Mechanics, Melbourne, pp. 1422–1442.
Marinos, P & Hoek, E 2001, ‘Estimating the geotechnical properties of heterogeneous rock masses such as flysch’, Bulletin of Engineering Geology and the Environment, vol. 60, pp. 85–92.
Marinos, P, Hoek, E & Marinos, V 2005, ‘Variability of the engineering properties of rock masses quantified by the geological strength index: the case of ophiolites with special emphasis on tunnelling’, Bulletin of Engineering Geology and the Environment, vol. 65, pp. 129–142.
Marinos, P, Marinos, V & Hoek, E 2007, ‘Geological Strength Index (GSI). A characterization tool for assessing engineering properties for rock masses’, in M Romana, A Perucho & C Olalla (eds), Underground Works Under Special Conditions, Taylor and Francis, Lisbon, pp. 13–21.
Palmström, A 1995, RMi - A Rock Mass Characterisation System for Rock Engineering Purposes, University of Oslo, Norway.
Palmström, A 2005, ‘Measurements of and correlations between block size and Rock Quality Designation (RQD)’, Tunnels and Underground Space Technology, vol. 20, pp. 326–377.
Pells, PJN, Bieniawski, ZT, Hencher, SR & Pells, SE 2016, ‘A reappraisal of the use of RQD in rock mass assessment’, in press.
Russo, G 2009, ‘A new rational method for calculating the GSI’, Tunnelling and Underground Space Technology, vol. 24, pp. 103–111.
Sonmez, H & Ulusay, R 1999, ‘Modifications to the geological strength index (GSI) and their applicability to stability of slopes’, International Journal of Rock Mechanics and Mining Sciences, vol. 36, pp. 743–760.
Sonmez, H & Ulusay, R 2002, ‘A discussion on the Hoek–Brown failure criterion and suggested modification to the criterion verified by slope stability case studies, Yerbilimleri, vol. 26, pp. 77–99.

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