Residual strength of granitic rocks

Abstract

When carrying out compressive tests on rock specimens, a stress plateau is typically attained following peak strength within a strain range a few times larger than the strain at peak strength. This stress level is commonly known as residual strength. A large database of these tests on granitic rock specimens has been compiled and analyzed in detail with the aim of improving understanding of the residual strength of this type of rock. It is observed that physical scale does not significantly change this residual strength. This stress threshold is also shown to be independent of the initial level of jointing in the rock volume. The implication of these findings is that residual strength derived from rock specimen testing can be potentially extended to rock mass scale, at least for granitic rocks. Three one-parameter residual strength models have been used to fit laboratory test residual strength data of granitic rocks, and all of them are shown to reasonably approximate the actual data. Additionally, the residual laboratory strength parameters of all the varied studied granitic rocks for varying scale and pre-jointing tend not to be very different, covering a limited range of values. Ultimately, the potential errors in simple excavation analysis that might result from a priori assumptions regarding the residual strength of granitic rock masses are quantified.