Nonlinear Creep Model for Rocks Considering Damage Evolution Based on the Modified Nishihara Model

Abstract

In general, the microdefects in rocks obey Weibull distribution. Based on the laws of statistics of microdefects in rocks, the relationship between the damage and the strain is established. Moreover, by considering characteristics of the viscoelastic–plastic and the damage evolution in rocks, a nonlinear creep model for rocks considering damage evolution is proposed to predict the creep behaviors of rocks based on the modified Nishihara model. In the proposed model, a dashpot element and a nonlinear viscoplastic body are added into the classical Nishihara model to simulate the accelerating creep stage of soft rocks. Moreover, the damage of rocks is considered in the process of creep. The effects of the shape parameter, the scale parameter, the peak stress, the peak strain, and the confining stress on the damage are investigated using the proposed method. The novel model is suitable to predict the creep behaviors of hard rocks and soft rocks simultaneously, and the difficulty to simulate the accelerating creep stage using the traditional creep model is overcome. To verify the robustness and precision of the proposed model, the creep behaviors of granite, coal, and red sandstone at different stresses are investigated. The predicted creep behaviors of soft and hard rocks using the proposed method are in good agreement with the experimental data, especially for the nonlinear accelerating creep stage.