Using a re-examination of published polyaxial rock test data, this paper reviews the differences between various polyaxial strength criteria fitted using customary Hoek-Brown empirical rock mass strength parameters. This paper compares the peak strength criteria in terms of error in the octahedral-, or π-plane, between peak strength determined under polyaxial stress conditions and the surface representing the criterion. Finally, this paper presents a discussion on the applicability of each of the strength criteria with respect to factors of safety computed in engineering design calculations.

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