The geological strength index: applications and limitations


The geological strength index (GSI) is a system of rock-mass characterization that has been developed in engineering rock mechanics to meet the need for reliable input data, particularly those related to rock-mass properties required as inputs into numerical analysis or closed form solutions for designing tunnels, slopes or foundations in rocks. The geological character of rock material, together with the visual assessment of the mass it forms, is used as a direct input to the selection of parameters relevant for the prediction of rock-mass strength and deformability. This approach enables a rock mass to be considered as a mechanical continuum without losing the influence geology has on its mechanical properties. It also provides a field method for characterizing difficult-to-describe rock masses. After a decade of application of the GSI and its variations in quantitative characterization of rock mass, this paper attempts to answer questions that have been raised by the users about the appropriate selection of the index for a range of rock masses under various conditions. Recommendations on the use of GSI are given and, in addition, cases where the GSI is not applicable are discussed. More particularly, a discussion and suggestions are presented on issues such as the size of the rock mass to be considered, its anisotropy, the influence of great depth, the presence of ground water, the aperture and the infilling of discontinuities and the properties of weathered rock masses and soft rocks.


Le Geological Strength Index (GSI) est un système de classification des massifs rocheux développé en mécanique des roches. Il permet d’obtenir les données relatives aux propriétés de masses rocheuses, données nécessaires pour des simulations numériques ou permettant le dimensionnement d’ouvrages:tunnels, pentes ou fondations rocheuses. Les caractéristiques géologiques de la matrice rocheuse ainsi que celles relatives à la structure du massif correspondant sont directement utilisées pour obtenir les paramètres appropriés relatifs à la déformabilité et la résistance de la masse rocheuse. Cette approche permet de considérer une masse rocheuse comme un milieu continu, le rôle des caractéristiques géologiques sur les propriétés mécaniques n’étant pas oblitèré. Elle apporte aussi une méthode de terrain pour caractériser des masses rocheuses difficiles à décrire. Après une décennie d’application du Geological Strength Index et de ses variantes pour caractériser des masses rocheuses, cet article tente de répondre aux questions formulées par les utilisateurs concernant le choix le plus approprié de cet index pour une large gamme de massifs rocheux. Des recommandations quant à l’usage du GSI sont données et, de plus, des cas où le GSI n’est pas applicable sont discutés. Plus particulièrement, des suggestions sont apportées sur des questions relatives à la taille de masse rocheuse à considérer, son anisotropie, l»influence des grandes profondeurs, la présence d’eau, l’ouverture et le remplissage des discontinuités ainsi que les propriétés des masses rocheuses altérées et des roches tendres.

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  1. 1.

    A simple search for “geotechnical baseline report” on the Internet will reveal the extent of this interest.


  1. Barton NR, Lien R, Lunde J (1974) Engineering classification of rock masses for the design of tunnel support. Rock Mech 6(4):189–239

    Google Scholar 

  2. Bieniawski ZT (1973) Engineering classification of jointed rock masses. Trans S Afr Inst Civ Eng 15:335–344

    Google Scholar 

  3. Brown ET (ed) (1981) Rock characterization, testing and monitoring—ISRM suggested methods. Pergamon, Oxford, pp 171–183

    Google Scholar 

  4. Cai M, Kaiser PK, Uno H, Tasaka Y, Minami M (2004) Estimation of rock mass strength and deformation modulus of jointed hard rock masses using the GSI system. Int J Rock Mech Min Sci 41(1):3–19

    Article  Google Scholar 

  5. Chandler RJ, de Freitas MH, Marinos P (2004) Geotechnical characterization of soils and rocks: a geological perspective. Advances in geotechnical engineering: the Skempton conference, vol 1, Thomas Telford, London, pp 67–102

    Google Scholar 

  6. Cheng Y, Liu SC (1990) Power caverns of the Mingtan Pumped Storage Project, Taiwan. In: JA Hudson (ed) Comprehensive Rock Engineering, vol 5, pp 111–132

  7. Cundall P, Carranza-Torres C, Hart R (2003) A new constitutive model based on the Hoek–Brown criterion. In: Brummer et al. (eds) Proceedings of the 3rd international symposium on FLAC and FLAC3D numerical modelling in Geomechanics, Sudbury, October 21–24, pp 17–25

  8. Deere DU (1964) Technical description of rock cores for engineering purposes. Rock Mech Eng Geol 1(1):17–22

    Google Scholar 

  9. Diederichs MS, Kaiser PK, Eberhardt E (2004) Damage initiation and propagation in hard rock during tunnelling and the influence of near-face stress rotation. Int J Rock Mech Min Sci 41(5):785–812

    Article  Google Scholar 

  10. Essex RJ (1997) Geotechnical baseline reports for underground construction. American Society of Civil Engineers, Reston

    Google Scholar 

  11. Hoek E (1994) Strength of rock and rock masses. News J ISRM 2(2):4–16

    Google Scholar 

  12. Hoek E, Brown ET (1980) Underground excavations in rock. Institution of Mining and Metallurgy, London

    Google Scholar 

  13. Hoek E, Brown ET (1997) Practical estimates of rock mass strength. Int J Rock Mech Min Sci Geomech Abstr 34:1165–1186

    Article  Google Scholar 

  14. Hoek E, Karzulovic A (2000) Rock mass properties for surface mines. In: Hustralid WA, McCarter MK, van Zyl DJA (eds) Slope stability in surface mining. Society for Mining, Metallurgical and Exploration (SME), Littleton, pp 59–70

    Google Scholar 

  15. Hoek E, Wood D, Shah S (1992) A modified Hoek–Brown criterion for jointed rock masses. In: Hudson JA (ed) Proceedings of the rock mechanic symposium. International Society of Rock Mechanics Eurock” 92, British Geotechnical Society, London, pp 209–214

  16. Hoek E, Marinos P, Marinos V (2005) Characterization and engineering properties of tectonically undisturbed but lithologically varied sedimentary rock masses under publication. Int J Rock Mech Min Sci

  17. Hoek E, Kaiser PK, Bawden WF (1995) Support of underground excavations in hard rock. AA Balkema, Rotterdam

    Google Scholar 

  18. Hoek E, Marinos P, Benissi M (1998) Applicability of the geological strength index (GSI) classification for weak and sheared rock masses—the case of the Athens schist formation. Bull Eng Geol Env 57(2):151–160

    Article  Google Scholar 

  19. Hoek E, Caranza-Torres CT, Corcum B (2002) Hoek–Brown failure criterion-2002 edition. In: Bawden HRW, Curran J, Telsenicki M (eds) Proceedings of the North American Rock Mechanics Society (NARMS-TAC 2002). Mining Innovation and Technology, Toronto, pp 267–273

  20. Knill J (2003) Core values (1st Hans-Closs lecture). Bull Eng Geol Env 62:1–34

    Google Scholar 

  21. Marinos P, Hoek E (2000) GSI: a geologically friendly tool for rock mass strength estimation. In: Proceedings of the GeoEng2000 at the international conference on geotechnical and geological engineering, Melbourne, Technomic publishers, Lancaster, pp 1422–1446

  22. Marinos P, Hoek E (2001) Estimating the geotechnical properties of heterogeneous rock masses such as flysch. Bull Eng Geol Env 60:82–92

    Article  Google Scholar 

  23. Sonmez H, Ulusay R (1999) Modifications to the geological strength index (GSI) and their applicability to the stability of slopes. Int J Rock Mech Min Sci 36:743–760

    Article  Google Scholar 

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Marinos, V., Marinos, P. & Hoek, E. The geological strength index: applications and limitations. Bull Eng Geol Environ 64, 55–65 (2005).

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Mots clés

  • Geological Strength Index
  • Massif rocheux
  • Structure géologique
  • Propriétés mécaniques
  • Conditions d»utilisation du GSI


  • Geological Strength Index
  • Rock mass
  • Geological structure
  • Mechanical properties
  • Selection of the GSI