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, https://doi.org/10.36487/ACG_rep/1604_32_Duran
(https://papers.acg.uwa.edu.au/p/1604_32_Duran/)
Abstract: 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