Validity of continuous-failure-state unloading triaxial tests as a means to estimate the residual strength of rocks

The residual strength of rocks and rock masses is an important parameter to be constrained for analysis design purposes in many engineering applications. A envelope principal stress space typically developed using data obtained from compression tests on different specimens the same type. In this study, we examined potential use continuous-failure-state testing concept as a means constrain limited number specimens. Specifically, cylindrical three types (granodiorite, diabase, Stanstead granite) were unloaded at state such that full each individual specimen was obtained. Using model introduces single new (the index, or RSI), results unloading compared conventionally envelopes. Overall, found consistent with conventional data. However, it identified primary factor limiting accurate characterization given type not amount specimen, but variety available characterize inherent variability unit interest. Accordingly, estimation only recommended when very (i.e. < 5).