Abstract
It is generally accepted that the strength of rock is determined by the presence of flaws, usually known as Griffith cracks. However, the various criteria based on this and other concepts fail to describe adequately the strength of rock under a general system of polyaxial compressive stresses. In particular, no account is taken of the intermediate principal stress. In addition, these various strength criteria usually attribute the onset of failure to cracks of a particular orientation. In this paper a new criterion is proposed, based on the additional energy stored around Griffith cracks due to the sliding of crack surfaces over each other. The predictions of strength based on this concept are in general agreement with the acknowledged behaviour of rock under uniaxial and triaxial stress systems. However, it is shown that in polyaxial compression, the intermediate stress has a pronounced and predictable effect. It also shows that cracks over a wide range of orientations contribute to the failure process; the limits being determined solely by the coefficient of sliding friction between crack surfaces. The polyaxial compressive strength of a rock can be predicted from a knowledge of its uniaxial strength, and the coefficient of sliding friction between its crack surfaces.
Published Version
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