Creep characteristics and prediction of creep failure of rock discontinuities under shearing conditions

Shear creep is one of the most important mechanical behaviors of rock discontinuities. The creep mechanism and prediction of starting point of the accelerating creep stage are vital for establishing the creep model and predicting creep failure. In this study, a series of multi-step creep tests are conducted. The three creep stages of shear creep tests are investigated in detail, and a method for predicting the accelerating creep stage is proposed. Distinct nonlinear and local fluctuations caused by cracking are observed in the creep curve. To describe the transition creep stage and steady creep stage, an empirical creep model is established, and the creep characteristics related to the joint roughness coefficient (JRC) and the normal stress are explored in detail using the model's parameters. The creep process can be described as involving the JRC resistance weakening and frictional resistance compensation, and a model also established to describe this process. The frictional resistance cannot compensate for the loss of JRC resistance; consequently, creep failure occurs. The starting point of the accelerating creep stage can be predicted by combining the JRC weakening and frictional mobilization model and the empirical creep model. A new method for determining long-term strength is also proposed based on the relationships between the starting point creep deformation and the shear creep stress.