A study of the scale effect influencing the shear strength of a large natural discontinuity

D. Casagrande, O. Buzzi, A. Giacomini

In the proceedings of: GeoOttawa 2017: 70th Canadian Geotechnical Conference; 12th joint with IAH-CNC

Session: Rock Mechanics II

ABSTRACT: The shear strength of rock discontinuities is known to be scale dependent. However, most of the studies having investigated this topic are based on relatively small specimens. Only a limited number of published data pertain to surfaces larger than 1 m2 and not all of them show a clear scale effect. The present research brings new insights into the effect of discontinuity size on its shear strength. A large surface, of about 2 m per about 2 m, was accurately surveyed using photogrammetry and its shear strength was estimated using a new semi-analytical mechanistic model. Sub-surfaces of various size and shapes were selected from the original large surface in order to quantify the possible scale effect. The results show that the surveying resolution is critical and that the way shear strength is expressed can either reveal or hide the existence of a scale effect.

RÉSUMÉ: La r”sistance au cisaillement des discontinuit”s rocheuses est connue pour ’tre sujet ‹ lÕeffet d'”chelle. Cependant, la plupart des ”tudes ayant ”tudi” ce sujet sont bas”es sur des sp”cimens relativement petits (moins de 300 mm de taille). Tr‘s peu dÕ”tudes contiennent des r”sultats sur des surfaces sup”rieures ‹ 1 m2 et lÕeffet dÕ”chelle nÕapparaflt pas toujours de fa“on ”vidente. Cette ”tude apporte de nouveaux ”l”ments sur l'effet dÕ”chelle appliqu” ‹ la r”sistance au cisaillement des discontinuit”s rocheuses. Une grande surface, d'environ 2 m par 2 m, a ”t” relev”e avec pr”cision en utilisant la photogramm”trie et sa r”sistance au cisaillement a ”t” estim”e ‹ l'aide d'un nouveau mod‘le m”canistique semi-analytique. Des surfaces de diff”rentes tailles et formes ont ”t” choisies dans la grande surface d'origine afin de quantifier l'effet d'”chelle possible. Les r”sultats montrent que la r”solution de mesure est critique et que la fa“on dont la r”sistance au cisaillement est exprim”e peut r”v”ler ou cacher l'existence d'un effet d'”chelle.

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Cite this article:
D. Casagrande; O. Buzzi; A. Giacomini (2017) A study of the scale effect influencing the shear strength of a large natural discontinuity in GEO2017. Ottawa, Ontario: Canadian Geotechnical Society.

@article{geo2017Paper162,author = D. Casagrande; O. Buzzi; A. Giacomini,title = A study of the scale effect influencing the shear strength of a large natural discontinuity,year = 2017}