Authors: Venter, J; Purvis, C; Hamman, J
Show More
Purchase Paper

Citation as:   ris   bibtex   endnote   text   Zotero

This paper presents an argument that the current accepted practice of obtaining the intact Hoek–Brown parameters σci and mi from single stage triaxial tests suffers from several drawbacks, for instance, many specimens are needed to obtain a single estimate of σci and mi, and specimen variability can result in difficult to interpret regression analyses. A solution is proposed in that multistage triaxial testing can be used, provided the peak compressive strengths needed are based on servo controlled termination of each testing stage based on real-time measurement of Poisson’s ratio. The paper proposes a procedure for determining peak strength for each stage and tests the proposed method against single stage triaxial tests. The paper finds that the approach is valid for practical purposes but also recommends further work.

Keywords: triaxial test, single stage, multi stage, Hoek-Brown

Venter, J, Purvis, C & Hamman, J 2016, 'Hoek–Brown mi estimation — a comparison of multistage triaxial with single stage triaxial testing', in PM Dight (ed.), Proceedings of the First Asia Pacific Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, pp. 289-299.

Cai, M 2009, ‘A simple method to estimate tensile strength and Hoek-Brown strength parameter mi of brittle rocks’, in M Diederichs & G Grasselli (eds), ROCKENG09: Proceedings of the 3rd CANUS Rock Mechanics Symposium, Toronto, pp. 1–12.
Cai, M 2010, ‘Practical Estimates of Tensile Strength and Hoek-Brown Strength Parameter mi of Brittle Rocks’, Rock Mechanics and Rock Engineering, pp. 167–184.
Cai, M, Kaiser, PK, Tasaka, Y & Minami, M 2007, ‘Determination of Residual Strength Parameters of Jointed Rock Massess using the GSI System’, International Journal of Rock Mechanics and Mining Sciences, pp. 247–265.
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, pp. 3–19.
Cawthorn, RG, Eales, HV, Walraven, F, Uken, R & Watkeys, MK 2006, The Bushveld Complex, MR Johnson, CR Anhaeusser & RJ Thomas (eds), The Geological Society of South African & The Council for Geoscience, Johannesburg.
Eberhardt, E 2012, ‘The Hoek-Brown Failure Criterion’, Rock Mechanics and Rock Engineering, vol. 45, pp. 981–988.
Gill, DE, Corthesy, R & Leite, MH 2005, ‘Determining the Minimal Number of Specimens for Laboratory Testing of Rock Properties’, Engineering Geology, vol. 75, pp. 29–51.
Hoek, E 2007, Practical Rock Engineering, Toronto,
Hoek, E, Carranza-Torres, C & Corkum, B 2002, Hoek-Brown Failure Criterion, University of Toronto, Toronto, pp. 267–273.
Hoek, E, Carter, TG & Diederichs, MS 2013, Quantification of the Geological Strength Index Chart, American Rock Mechanics Association, San Francisco.
ISRM (International Society for Rock Mechanics) 1983, Suggested Methods for Determining the Strength of Rock Materials in Triaxial Compression: Revised Version, International Society for Rock Mechanics.
Rocscience 2015, RocData, software, version 5.0, Rocscience Inc, Toronto,
Ruffolo, RM & Shakoor, A 2009, ‘Variability of Unconfined Compressive Strength in Relation to Number of Test Samples’, Engineering Geology, vol. 108, pp. 16–23.

© Copyright 2017, Australian Centre for Geomechanics (ACG), The University of Western Australia. All rights reserved.
Please direct any queries to or error reports to