![]() The method of research is based on books and articles published in authoritative publications and journals. In this paper we present outlines of these criteria and focus on the Hoek-Brown criterion. ![]() One of the most widely used empirical strength criterion for intact rock and rock masses is Hoek-Brown Criterion. The plane Griffith criterion which locates in theoretical group, express the uniaxial tensile strength in terms of the strain energy required to propagate micro cracks. The Mohr-Coulomb criterion expresses the relation between the shear stress and the normal stress at failure. And the last set of them is composed of two mentioned sets of failure criteria. The strength criteria of rock materials can be divided into three major groups: theoretical failure criteria, experimental and curve fitting based criteria. Nevertheless, as engineers, we should like some measure of the failure properties and the ability to predict when failure will occur. In both cases, the process is extremely complex and not subject to convenient characterization through simplified models. It is not clear exactly how a rock fails, either in terms of the precise details of each micro crack initiation and Propagation or in terms of the total structural breakdown as many micro cracks propagate and coalesce.
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