ESTIMATION AND VERIFICATION OF UNIAXIAL TENSILE STRENGTH OF SATURATED HARD ROCKS

The uniaxial tensile strength(UTS) of saturated rocks is not easy to obtain because of the difficulty in specimen preparation and test execution. To estimate the saturated rocks' UTS and analyze the water effects on its accuracy,we conducted a series of uniaxial compression and direct tension tests of two hard rocks,coupled with acoustic emission(AE)monitoring. Based on the Griffith theory and Hoek-Brown(H-B)criterion,crack initiation stress determined by crack volumetric strain curve was utilized to evaluate the UTS and H-B strength parameter m_i. The accuracy of estimation of these two parameters was analyzed by the spectrum characteristics of AE waveforms. Results show that,the method of crack initiation stress based on Griffith criterion is reliable to estimate the saturated hard rocks' UTS. The estimated values of dry hard rocks' UTS are smaller than those of experimental values. In comparison,the estimated saturated rocks' UTS is closer to the experimental value. This is mainly because the ductility and creep of hard rocks tend to increase after saturation,and more micro-tensile failures occur inside the rocks. The increase in m_i of saturated hard rocks is related to the growing micro-tensile failures. Moreover,the m_i can be used to describe the degree of the water-weakening effect. The estimation of rock UTS andm_i based on Griffith's theory and crack initiation stress can be applied in the early design of rock mass engineering practice.