Nonlinear Unloading Rheological Model For Hard Brittle Rock Mass And Its Engineering Application

Large hydropower engineering project has long service period for its special function, and the rock mass with high strength is generally in a certain condition of high three-dimensional stress, so the high dam slope rock mass engineering will arise obvious instantaneous deformation and aging deformation from excavation unloading, scholars both at home and abroad have been paid attention to the phenomenon of unloading rheological damage about rock mass, but the unloading rheological mechanical characteristics and failure mechanism about hard brittle rock mass are still insufficient. So, on the basis of previous studies, we studied the unloading rheological mechanical properties of hard brittle rock mass systematically by means of laboratory experiment, theoretical analysis and numerical modeling. An nonlinear unloading rheological constitutive model that can describe the deformation time effect evolution law of hard brittle rock are established based on the test result. As the application of the test and theory research results, the numerical calculation analysis is conducted for Dagangshan hydropower station high dam slope engineering through the large-scale finite element software ANSYS.The main research contents and results are as follows:（1） Triaxial test and triaxial unloading rheological test of both the granite from Mengdigou and the diabase from Dagangshan are carried out by using automatic rock triaxial rheological servo device. The basic mechanical characteristics and unloading rheological mechanical properties of hard brittle rock are studied, and the unloading rheological deformation law, unloading rheological rate change law, unloading rheological strength change law and unloading rheological failure mode are mainly studied.（2） SEM test of destroy section is carried out by using SU₇0 thermal field emission scanning electron microscopy. The damage mechanism of hard brittle rock are sdudied, and the relationship between the change of mesoscopic structure and the macroscopic damage forms is obtained.（3） The unloading long-term strength of hard brittle rock mass is analysed by steady-state creep rate "intersection method", and the threshold value of long-term strength for hard brittle rock mass is obtained, which can reflect the law of unloading rheological long-term strength for hard brittle rock.（4） A nonlinear unloading rheological model for hard brittle rock based on the fractional order calculus theory is established, and the one-dimensional constitutive equation and the three-dimensional expression are derived. This model can describe test features of hard brittle rock, including the steady deformation during steady-state creep stage, the obvious "dilatancy" during accelerating creep stage and the "brittle failure features is more obvious".（5） The nonlinear unloading rheological model is developed by completing the development program combined with the development platform of ANSYS. The comparison between the numerical calculation curve and creep test curve verifies the validity of the development program.（6） The three-dimensional numerical analysis of the long-term stability of slope excavation for Dagangshan hydropower station high slope engineering is accomplished by using the development program of the nonlinear unloading rheological model for hard brittle rock.