| Rock mass deformation is a time-dependent process, especially for soft rock, its deformation is significantly timeliness, the widely used elastic-plastic theory can’t describe or predict this process, but rheological theory is a better method to overcome this drawback. It possesses important significance for practical engineering to describe the time-dependent mechanical characterization and behavior of rock mass. With the chlorite segment of west diversion tunnel of Jingping-II hydroelectric station as engineering background, based on experiment and field measurement results, this paper investigates the constitutive model suitable for describing rheological characteristics of tunnel with soft rock, and assigned some numerical analysis by using the constitutive model, and discussed the method for rheological parameters identification. The main research research content containing some aspects as following:(1) Microstructure features and elemental composition were analysised by scanning electron microscopy and energy dispersive. In order to know about deformation and failure characteristics of chlorite in high groundwater level, the mechanical characteristics of chlorite with drying and saturation state were studied by rock rigid test machine.(2) A new four-element nonlinear viscoelasto-plastic rheological model based on an expression with a fractional calculus form is proposed, by using the Riemann-Liouville fractional calculus theory. The constitutive equation and creep equation of the model are given. The prediction of the model on existed data is examined, and the result shows that the nonlinear rheological model can effectively describe three steps of rock creep, and plays a role to reduce the element number and parameters in the model.(3) Attenuation equation were proposed to describe rheological parameter decreased with time or strain in three-stage creep process, and improved three-parameter H-K damage model was established based on the attenuation equation. The prediction of the model on existed data is examined, and the result shows that both two damage models can effectively describe three steps of rock creep.(4) The viscoelastic displacement analytic equation of tunnel was derived based on fractional Maxwell model, and considers the influence of tunnel face. Through comparing with analytical solution of Burgers model, and the result shows that tow models can coincident with each other in specific time quantum.(5) Improved three-parameters H-K (generalized kelvin) damage three-dimensional constitutive model with rheological parameters decreased with equivalent strain was proposed, based on three steps of rock creep, which can effectively reflect elastic deformation and creep deformation of soft rock in different stress level. The method of improved model applied to finite difference program FLAC3D was given, that dynamic evaluation and correction rheological parameters in calculation process by using embedded FISH language.(6) Based on Improved three-parameters H-K constitutive model, creep deformation characteristics of soft tunnel with different deep overburden or lateral pressure coefficient, tunnel face effect on rheological, the influence of construction stopping time on rheological, the influence of bench cut method on rheological, were investigated by using FLAC3D.(7) In concert with the chlorite creep test and field measurement data, rheological parameter inversion methods were studied by using particle swarm optimization algorithm. Error back propagation neural network and particle swarm optimization algorithm are combined with finite difference program FLAC D and the uniform design method, then acomprehensive back analysis method for rheological parameters of engineering rock mass is established.(8) In concert with the engineering construction and improved three-parameters H-K constitutive model, the influence of special support (prestressed anchor cable and anchor bar pile) on rheological of soft rock tunnel with deep overburden were analyzed by using FLAC3D, and the result shows that prestressed anchor cable can plays a role to decrease the local deformation, and lower bench would be more security after applied anchor bar pile. |
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