Characterization of failure loads and failure modes in schist from indirect tension tests

Planes of weaknesses which are present within laboratory rock specimens will influence strength, stiffness, and failure mode. For indirect tension testing, the orientation of planes of weakness can be described using both face and edge orientations. Schist specimens obtained from vertical core drilling and sampling were tested in indirect shear. Failure load was related to face schistosity orientation, because edge schistosity orientation could not be controlled, and failure mode. Three failure modes were identified: axial failure where the failure plane cut across schistosity, in-specimen failure where the failure plane was coincident with schistosity and the failure plane did not intersect the specimen face, and out-of-specimen failure where the failure plane was coincident with schistosity and the failure plane intersected the front or back face the specimen. Failure loads from axial failures were statistically significantly different that failure loads occurring along schistosity. Failure loads occurring along schistosity were not statistically significantly different from each other.