Effect of micro-parameters on the Hoek-Brown strength parameter m _i for intact rock using particle flow modeling

Hoek-Brown strength criterion has been used for analysis of a wide range of problems in rock mechanics and rock engineering. For intact rock, the criterion is mainly controlled by the strength parameter m_i which is empirical and developed by trial and error. By representing intact rock as a densely packed cemented granular material, its mechanical behavior can be modeled using the particle flow modeling. In this paper, the three dimensional particle flow code PFC3D is used to conduct numerical tests on intact rock and investigate the effect of micro-parameters on the strength parameter m_i. The micro-parameters which may affect the strength parameter m_i, such as particle size, contact model type, the normal and shear strength are studied respectively. The results show that the particle size only has minor influence on the strength parameter m_i and its effect can be simply ignored. The contact model type and the contact normal to shear strength ratio, however, both have major effect on the strength parameter m_i. The parallel-bond model gives higher m_i values than the contact-bond model. When the normal to shear strength ratio is smaller than 1, higher shear strength leads to large increase of parameter m_i.