Research On Rheological Model Based On Thermodynamics With Internal State Variables And Long-term Stability Of Rock Mass Structures

Some world-class rock engineering are embedded in projects in China, like construction of hydraulic and hydropower engineering, underground storage of oil and gas, mining of coal and mineral. These rock engineering show huge project scale, encounter complicated geological envir onment and give rise to severe disturbance. Natural rocks, which are disturbed severely by construction of project, represent time-dependent redistribution of stress and deformation that directly affects the normal operation and long-term stability of the project. In this paper, the rules of non-equilibrium evolution and long-term stability of disturbed rock mass are studied from the perspective of dynamic evolution. Rheological model and analytical method of long-term stability for rock mass structure are the core works in this paper. The major research contents and achievements are listed as following:(1) The 3-D geomechanical model test of a high arch dam with treatments was conducted, and the stability of the arch dam is analyzed. The reinforcement effects of foundation treatments are evaluated by comparing the results of model tests with and without foundation treatments in term of stress, deformation, failure mode and overload safety factors.(2) A rheological model is developed based on thermodynamics with internal state variables. The physical meanings of internal state variables(ISV) embedded in the proposed viscoelastic and viscoplastic constitutive equations are explored. The validity and rationality of the proposed model is validated by creep test of analogue material.(3) Stress relaxation constitutive equation is derived. The equivalence of creep and stress relaxation is illustrated from the perspective of dynamic evolution of structure within material sample, and the physical-mechanical mechanism which control creep and relaxation is expored under different external constraints, namely, the internal consistency of creep and stress relxation is clarified.(4) Thermodynamic stability of material system is revealed based on the Lyapunov’s second method for stability. It is summarized the properties and rules of different thermodynamic processes corresponding time-dependent deformations. The non-equilibrium evolution laws and stability of continuum structures with constant loads and displacement boundary are revealed, and the quantitative evaluation indexes and definite criteria are proposed for analyzing the long-term stability of rock mass structure.(5) The calculation programs, called CTV-E and CTV-P, are developed through second development interface of FLAC3 D software combined with proposed creep model. The developed programs are applied for deep-buried double tunnels and left abutment slope of Jinping arch dam project. It is obtained that the curves between integral value of energy dissipation rate in domain(Ω) and its time derivative(Ω) and time, which can be used to analyze the non-equilibrium evolution rules and long-term stability of rock mass structure. These results also reveal the weakness regions within structure in the process of long-term deformation.