Gsi geotechnical system index

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Bull Eng Geol Environ (2005) 64: 55–65 DOI 10.1007/s10064-004-0270-5

ORIGINAL PAPER

V. Marinos P. Marinos E. Hoek

The geological strength index: applications and limitations

Received: 7 September 2004 Accepted: 9 October 2004 Published online: 2 February 2005 Ó Springer-Verlag 2005

V. Marinos (&) Æ P. Marinos School of Civil Engineering, Geotechnical Department, National TechnicalUniversity of Athens, 9 Iroon Polytechniou str., 157 80 Athens, Greece E-mail: vmarinos@central.ntua.gr E-mail: marinos@central.ntua.gr E. Hoek Consulting Engineer, Vancouver, Canada E-mail: ehoek@attglobal.net

Abstract 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 bythe 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, thepresence of

ground water, the aperture and the infilling of discontinuities and the properties of weathered rock masses and soft rocks. ´ ´ Resume Le Geological Strength In` dex (GSI) est un systeme de classification des massifs rocheux ´ ´ ´ developpe en mecanique des roches. ´ Il permet d’obtenir les donnees rel´ ´ atives aux proprietes de masses ´ ´ rocheuses, donnees necessaires pour ´ dessimulations numeriques ou permettant le dimensionnement d’ouvrages:tunnels, pentes ou fondations ´ rocheuses. Les caracteristiques ´ geologiques de la matrice rocheuse ` ainsi que celles relatives a la structure du massif correspondant sont ´ directement utilisees pour obtenir les ` ´ ` parametres appropries relatifs a la ´ ´ ´ deformabilite et la resistance de la masse rocheuse. Cette approche ´ permetde considerer une masse rocheuse comme un milieu continu, ´ ´ le role des caracteristiques geologiˆ ´ ´ ´ ques sur les proprietes mecaniques ´ ` ´ n’etant pas oblitere. Elle apporte ´ aussi une methode de terrain pour ´ caracteriser des masses rocheuses ` ´ ` ´ difficiles a decrire. Apres une decennie d’application du Geological Strength Index et de ses variantes ´ pour caracteriser des massesroche´ uses, cet article tente de repondre ´ aux questions formulees par les utilisateurs concernant le choix le ´ plus approprie de cet index pour une large gamme de massifs rocheux.

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` Des recommandations quant a ´ l’usage du GSI sont donnees et, de plus, des cas ou le GSI n’est pas ` ´ applicable sont discutes. Plus par` ticulierement, des suggestions sont ´ apportees sur des questionsrelatives ` ` a la taille de masse rocheuse a con´ siderer, son anisotropie, l»influence ´ des grandes profondeurs, la presence

d’eau, l’ouverture et le remplissage ´ des discontinuites ainsi que les pro´ ´ ´ ´ prietes des masses rocheuses alterees et des roches tendres. Keywords Geological Strength Index Æ Rock mass Æ Geological structure Æ Mechanical properties Æ Selection of the GSI

´ Mots...
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