A new approach to avoid the scale effect when predicting the shear strength of large in situ discontinuity

O. Buzzi, D. Casagrande, A. Giacomini, C. Lambert, G. Fenton

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

Session: Rock Mechanics II

ABSTRACT: Estimating the shear strength of large in situ discontinuities is far from trivial. One option is to estimate the peak shear strength using BartonÕs empirical criterion based on the Joint Roughness Coefficient (JRC) that can be measured on a trace but JRC is known to be scale dependent. It is also possible to retrieve cores and perform some direct shear tests on the surface but such results would require some form of up-scaling, which is still unresolved. A new approach was developed to predict shear strength of large discontinuities directly at the intended scale, avoiding changes of scale and, as a result, minimizing the scale effect. The approach is based on the rigorous application of random field theory and relies on stochastic predictions. This paper presents the validation of the approach, which includes the presentation of a new analytical model for shear strength that underpins the application of stochastic predictions.

RÉSUMÉ: L'estimation de la r”sistance au cisaillement des discontinuit”s rocheuses in situ nÕest pas ais”. Une option consiste ‹ estimer la r”sistance au cisaillement en utilisant le crit‘re empirique de Barton bas” sur le coefficient de rugosit” JRC, mesurable sur une trace. Toutefois, le JRC est sujet ‹ lÕeffet dÕ”chelle. Il est ”galement possible d'effectuer des essais de cisaillement direct sur des ”chantillons rocheux, mais ceci implique de proc”der ‹ un changement dÕ”chelle pour que ces r”sultats soient pertinents. Une nouvelle approche a ”t” d”velopp”e pour pr”dire la r”sistance au cisaillement de grandes discontinuit”s directement ‹ l'”chelle du massif rocheux, en ”vitant les changements d'”chelle et, par cons”quent, un effet d'”chelle. La nouvelle approche repose sur l'application rigoureuse de la th”orie des champs al”atoires et sur lÕutilisation de pr”dictions stochastiques. Cet article pr”sente la validation de la nouvelle approche et celle d'un nouveau mod‘le analytique de pr”diction de la r”sistance au cisaillement.

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