Study On Constitutive Model And Damage-induced Permeability Change For Low-porosity Rock Base On Micrmechanics

Coupled THM problem has become an important branch of modern rock mechanics, this issue related to many project applications, such as: disposal of nuclear waste, secondary exploitation of petroleum, underground sealing of carbon dioxide, and safety assessment of high dam foundation etc. Though certain advance has been made on mathematic model, in situ experiment and computer code at present, the coupling process of intact rock, fracture rockmass and signle fracture still need proceed. Scholars still work on the coupling model that could describe the deformation and permeability chang during triaxial compression especially hoped the model could describe the load induced permeability anisotropic chang. In this thesis, we study a special kind of rock: low porosity rock, the constitutive model and permeability change model is investigated by using micromechanical theory. The main research content and result is as follows:(1) The constitutive modeling theory, permeability change model and numerical method in rock mechanics are summarized. Continue damage theory and micromechanical damge theory is compared; the reason of choosing micromechanical damage theory to establish constitutive model and permeability evolution model is stated. The deficiency in the current permeability change model is pointed out, then, the research thought and method in the thesis is put forward.(2) The micromechanical model for low porosity rock is established in strain-based formulation. Firstly, the main character of rock deformation in triaxial compression is summaried and a explanation in micro structure level is given as a goal of micromechanical. The procedure of modeling, determination of REV scale and conceptual model of rock: low porosity rock composed of rock host and microcracks is represented. According to stress condition, the microcracks are divided into two classes: tensile microcrack and shear microcrack. The criterion of tensile/shear is established and expressed in the strain space. The criterion of tensile microcrack propagation and evolution equation is deduced based on micromechanics analysis. The fourth order homogeneous stiffness tensor and tagent homogeneous stiffness are deduced by using energy theory.(3) A comment of criterions of microcrack sliding is given; then a new sliding criterion in this thesis is put forward. Crack sliding induced microcrack surface normal dilation and normal dilation induced microcrack further self-similar propagation are considered, the ineracting of sliding and propagation is clarified. The fourth-order tangent homogeneous stiffness tensor of shear microcrack is deduced, and at last the constitutive model of low porosity is expressed in increment formulation though unit sphere surface integral. The computer code that simulates the triaxial experiment of tension and compression is developed, and sensibility of each model parameter is analyzed, the computation result is analyzed and explained in detail.(4) The regularity pheonomenon of permeability change in the triaxial compression process is generalized, and the conception model that describes the four stage of permeability evolution is presented, which is the goal of modeling. The two factor influencing rock permeability: aperture of micro fracture and connectivity of micro fracture system is discussed. The change fracture aperture is considered consis of three parts: elastic compression, shear sliding induced normal dilatation and fracture propagation induced normal dilatation. The evolution equation of fracture aperture in the strain space is deduced, and the evolution equation of connectivity in the damage process is derived. The code that analyzes the sensibility of model parameters in the permeability change model is programmed, and computation result is explained with micro fracure kinesis.(5) The constitutive model and permeability change model is verified through rock sample experiment. Marble sample in Nanjing area is selected to triaxial test, and the test result is simulated by the micro constitutive model suggested in the thesis. The simulation confirms the correct of the model. The universality of the model is proved by simulation of test of granite and sandstone in other literatures. Experiment results of granite permeability in triaxial compression is analyzed and simulated by the permeability change model in the thesis. The simulation result is compared with the result of Souley, and the commentary is given. The experiment result of basalt in Luogu area during the triaxial compression is analyzed and simulated, and the commentary is given.(6)Developed the calculation code of constitutive and permeability change model by using ABAQUS's user define material routine interface. Three tunnel's excavation about 420 meters below underground which located in URL Canada is simulated using promoted model. Results of simulation is discussed and compared with measured.