Non-stationary Nishihara model in the particle flow code

In order to accurately simulate the whole process of rock creep and explore the generation and development of mirco-fractures from the meso-level, a visco-elastoplastic Nishihara rheological constitutive model is developed in the two-dimensional particle flow code (PFC2D). Then a non-stationary Nishihara model including two non-stationary elements is put forward in this article. A constitutive equation and a creep equation are derived based on the non-stationary Nishihara model. The user-defined Nishihara constitutive model is called in PFC2D, and a numerical sample whose strength properties are the same as those of a real rock specimen is acquired by parameter testing. Using the data of uniaxial creep tests in laboratory, the non-stationary parameters are back analyzed in Matlab. At last, uniaxial creep tests are simulated using the stationary and non-stationary models, and micro-fractures are monitored. A comparison of these results show that the stationary model can only be used to describe the decay and steady stages, while the non-stationary model is also applicable to the accelerated stage, and thus can simulate the whole process of rock creep. Accelerated creep results from the accelerated development of mirco-fractures and leads to shear failure. ©, 2015, The Editorial Board of CHINESE JOURNAL OF ENGINEERING. All right reserved.