A simple approximation to estimate the Hoek-Brown parameter 'mi' for intact rocks

A very useful approximation for the estimation of the Hoek-Brown material constant no; is presented in this study and the basic logic behind it is evaluated in detail. The study clearly indicates that the Hoek-Brown material constant m(i) can be approximately predicted from the ratio between the uniaxial compressive strength and tensile strength of brittle intact rocks. By introducing the brittleness ratio of sigma(c)/sigma(t) into the generalized Hoek-Brown failure equation instead of the material constant m which, actually; has a fundamental importance, a practical formulation is suggested for this commonly employed failure criterion.