Laboratory creep tests for time-dependent properties of a marble in Jinping II hydropower station

In order to investigate the time-dependent behaviors of deep hard rocks in the diversion tunnel of Jinping II hydropower station, uniaxial creep tests were carried out by using the triaxial testing machine RC-2000. The axial compressive load was applied step by step and each creep stage was kept for over several days. Test results show that: (1) The lateral deformation of rock specimens is 2–3 times the axial compressive deformation and accelerates drastically before damage, which may be employed as an indicator to predict the excavation-induced instability of rocks. (2) The resultant deformation changes from compression to expansion when the Poisson’s ratio is larger than 0.5, indicating the starting point of damage. (3) In the step-loading stages, the Poisson’s ratio approximately remains constant; under constantly imposed load, the Poisson’s ratio changes with elapsed time, growing continuously before the specimen is damaged. (4) When the applied load reaches a certain threshold value, the rock deteriorates with time, and the strength of rocks approximately has a negative exponent relation with time. (5) The failure modes of the deep marble are different in long- and short-term loading conditions. Under the condition of short-term loading, the specimen presents a mode of tensile failure; while under the condition of long-term loading, the specimen presents a mode of shear failure, followed by tensile failure.