Effect of artificial joints on the mechanical response of a granitic rock

The scale effect is still an unsolved problem on rock mechanics discipline, there are some empirical approaches that work reasonably well, but lack of knowledge of the affecting parameters. For instance, Hoek-Brown generalized failure criterion is a good and practical way to estimate rock mass strength. It considers the quality of the rock mass and, indeed, the characteristics of the discontinuities as a whole, by means of GSI, but it is not known how the different parameters of the discontinuities affect the rock mass strength. Trying to bring some light into the topic, some authors have argued about the necessity to split scale effect into size effect and structure effect. Size effect has been reasonably solved by means of classic or novel approaches, although there are some issues about the range of applicability of each approach. Structure effect has been addressed mainly by means of synthetic non-rock material specimens, and only a few authors have tried to prepare and test actual-rock jointed specimens. The current study revisits the issue of the presence of artificial joints in laboratory rock specimens, although it is mainly focused on testing the equipment capabilities of the Rock Mechanics Laboratory of the Catholic University of the North in northern Chile. Two series of specimens of a local granitic rock (Loa’s granite) are tested. First series includes five intact specimens tested under unconfined conditions, and second series includes eleven jointed specimens featuring two sets of discontinuities tested under triaxial conditions. Tests results show a clear dependence of strength on jointing, and that the strain localization occurs mainly on the artificial discontinuities.