Rock failure criteria

Based on the found regular patterns of plastic deformation and failure of rocks, an analytical plasticity and strength criterion is proposed, compared with the known failure criteria by Coulomb and Hoek–Brown, comprehensively analyzed and verified. A classification of rocks by features of plastic deformation is presented. Benefits and disbenefits of the existing rock failure criteria are considered. A novel view on the mechanisms of plastic deformation of rocks in the phase of strengthening is put forward and discussed. It is highlighted that plastic deformation is translational-and-rotational nearby planes of shear, and the result of such behavior is higher strength of rocks (strengthening) and dilatancy. That is, micro-cracks which appear at the stage of deformation-induced strengthening keep off turning into fullfledged sliding surfaces intersecting the whole sample when the stress deviator is raised. This is connected with the stress redistribution at the crack tips (growth of the normal stresses), caused by the turn of the plane of shear and by the elastic reaction pressure of side rocks, which, in its turn, leads to the closure of the crack mouths, and the crack cannot grow further. The article presents quantitative relations to find force factors which initiate dilatancy and turn of components in the medium, i.e. spotlight is on dynamics of the plastic deformation process. The authors come to a conclusion that the major drawback of the Coulomb criterion is low precision of failure prediction while the advantage is easy usability. Alternatively, the Hoek–Brown failure criterion offers a sufficiently accurate prediction of a failure envelope but, being empirical at bottom, provides no explanation of the physics or mechanics of plastic deformation. In this context, the proposed criterion is preferable as it determines the limit strength, limit elasticity and the plastic potential, as well as allows evaluating the process of plastic deformation in rocks.

Zhabko A. V. Rock failure criteria. MIAB. Mining Inf. Anal. Bull. 2021;(11-1):27—45. [In Russ]. DOI: 10.25018/0236_1493_2021_111_0_27.

Zhabko A. V., Dr. Sci. (Eng.), Associate Professor, Head of the Mine Surveying Department, zhabkoav@mail.ru, Ural State Mining University, ul. Kuibysheva 30, Yekaterinburg, 620144 Russia.

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