New accelerated rock creep model considering nonstationary viscosity coefficient

Abstract

Accelerated creep models are popular research topics in rock mechanics. By analyzing the variation in the viscosity coefficient in the accelerated creep stage and defining the viscoplastic internal variable, a general evolution law for the viscosity coefficient was revealed, and a widely applicable accelerated creep model was proposed. First, the creep test data of 24 rock types were collected and analyzed. Subsequently, the contrast between the strength decrease in the accelerated creep-subsequent failure stage and the post-peak strength decrease in the elastoplastic process was evaluated, and the viscoplastic internal variable in the accelerated creep stage was defined. Subsequently, the evolution function between the normalized viscosity coefficient and the viscoplastic internal variable was established. Based on the test data for different rocks, the predicted curves accurately captured the evolution of the normalized viscosity coefficient with the viscoplastic strain increment and confining pressure in the accelerated creep stage. A new accelerated creep model was constructed by modifying the linear viscoplastic part of the Nishihara model using an established evolution model of the viscosity coefficient. The model demonstrated agreement with the experimental data for different rocks and yielded results close to the monitored tunnel convergence data.