Gypsum Breccia Nonlinear Rheological Model And Finite Element Analysis

In this paper, the instantaneous deformation and failure characteristics, creep characteristics of gypsum breccias under different confining pressures and stress levels are studied by means of conventional triaxial compression tests and uniaxial and triaxial compression creep tests. The results show that gypsum breccias can display the creep properties of nonlinearity and acceleration under certain stress level. On the basis of polarization microscope analysis and scanning electron microscope analysis, the creep mechanism of gypsum breccias is also discussed.Based on statistical damage theory, the instantaneous damage constitutive relationship of gypsum breccias is studied. In consideration of the impact of damage threshold, a statistical damage constitutional equation is established. The theoretical calculated results are basically close to conventional test results. In the light of creep characteristics of gypsum breccias, a multiple rheological mechanics model is set up. With Quasi-Newton fitting program written by the author, the rheological model parameters are fitted in accordance with creep test results and theirs variation regularities are analyzed under different stress levels. Based on the statistical damage evolution equation considering stress damage threshold and the multiple rheological model of gypsum breccias, the damage rheological constitutional model is established from hypothesis of strain equivalence. The calculated results of the model agree well with creep test results. This indicates that the damage rheological constitutional model put forward can effectively describe the nonlinear rheological property of gypsum breccias. On the basis of Kachanov's one-dimensional creep damage evolution equation, the rheological constitutional model is established which considering instantaneous damage and creep damage. The good agreement of theoretical data with test data shows that the creep damage evolution equation put forward is rational and the damage rheological constitutional model established can describe the accelerated creep stage of gypsum breccias well.Because of artificial neural network's good simulation of nonlinearity, the nonlinear rheological property of gypsum breccias is studied tentatively through neural network. The neural network model for rheology of rock is established under separate loading. Taking visco-elastoplastic model as an examination question, it is verified that the neural network rheological model is feasible and effective in describing rheological behavior of rock. In order to improve neural network rheological model's extrapolation ability of time, the idea of "segment extrapolation" is put forward. And in order to raise extrapolation stability of each segment, the method of "primary training" is proposed.