Abstract
For the purpose of evaluating rock mass stability around an underground opening, this paper proposes new strain criteria of rock and rock masses making use of the Hoek & Brown failure criterion, which has been widely accepted and utilized all over the world. One of the authors previously proposed the critical/failure strain, which has been used in tunnels or cavern constructions as a standard indicator of rock mass stability. It still has problems, however, that the critical/failure strain of an intact rock may not simply apply to rock masses and to the region of a large confining pressure. The results of this research imply that the new strain criterion for an intact rock can be made applicable to the region of a large confining pressure and to rock masses only in unconfined stress states. It should be noted, however, that the new criterion for rock masses is significantly larger than that for an intact rock in triaxial stress states.
