Creep behavior of fractured granite with different inclination angles

The creep phenomenon of inelastic deformation of surrounding rock may occur under the action of deep geological stress for a long period of time, potentially resulting in large-scale deformations or even instability failure of the underground engineering. Accurate characterization of the creep behavior of the surrounding rock is essential for evaluating the long-term stability and safety of high-level radioactive waste (HLW) disposal repositories. Although the laboratory creep tests of brittle undamaged rocks, such as granite, have been extensively performed, the creep characteristics of fractured surrounding rock under the multi-field coupling environment still require attention. In this study, a series of creep experiments was conducted on Beishan granite, which was identified as the optimal candidate surrounding rock for the disposal repository in China. The effects of various factors, including inclination angle of fractures, stress conditions, temperatures, and water content, were investigated. The experimental results show that the axial total strain increases linearly with increasing stress level, while the lateral total strain, axial and lateral creep strain rates increase exponentially. The failure time of saturated specimens fractured at 45° and 60° is approximately 1.05‰ and 0.84‰ of that of dry specimens, respectively. The effect of temperature, ranging from room temperature to 120 °C, is minimal, compared to the substantial variations in strain and creep rates caused by stress and water content. The creep failure of specimens fractured at 30° is dominated by rock material failure, whereas the creep failure of specimens fractured at 60° is dominated by pre-existing fracture slip. At a 45° fracture angle, a composite failure mechanism is observed that includes both rock material failure and pre-existing fracture slip.