STRENGTH BEHAVIOUR OF ANISOTROPIC ROCKS

Abstract

A number of strength criteria have been proposed for intact rocks by various researchers in the past. Among them, the Mohr—Coulomb strength criterion is the most popular and widely used strength criterion. The Mohr-Coulomb criterion, which is linear, was initially proposed for the determination of the intact rock strength in isotropic conditions. It is now well established that the strength behaviour of rock is non-linear. In the present study, the non-linear response in strength has been incorporated in the Mohr—Coulomb criterion. Barton's critical state concept for rocks has been used for this purpose. At critical confining pressure the gradient of the Mohr envelope becomes zero. The shear strength parameters c and 0, obtained from triaxial strength tests performed at low confining pressure, are directly used in the proposed equation to determine the triaxial strength of the rock at higher confining pressure. In this work a statistical analysis has been done by triaxial test data available from literature which gave the critical confining pressure roughly equal to r, where i is the uniaxial compressive strength of the rock test performed perpendicular to the plane of orientation. The proposed equation has been validated by the experimental values obtained from the database of anisotropic intact rocks and the predicted strength values obtained from proposed criteria has been found to be in good agreement with the database experimental triaxial results. The strength values are then compared with the strength values obtained from other strength criteria and the results of the present study have been found to be comparable and slightly better to the results obtained from the other strength criteria.