Employing frictional parameters in estimating the Hoek-Brown constant mi for intact rocks

An important parameter of the Hoek-Brown failure criterion for intact rock materials is m i , a dimensionless material constant that depends on the frictional characteristics of the component minerals. In this study a laboratory testing program was carried out in order to experimentally study the correlations between m i and two frictional parameters: (a) the sliding friction angle which is determined from direct shear tests on pre-fractured rock specimens and (b) the Mohr-Coulomb internal friction angle which is determined from triaxial compression strength tests conducted at low confining stresses. We carried out direct shear tests on rough tension joints of ten fresh, low porosity (