Study On Constitutive Model Of Coupled Damage-Permeability Process Of Brittle Rock Based On Micromechanics.

The coupled process of stress and seepage in rock is one of the most important branches of rock mechanics, which focuses on the interaction of rock and the related environment. Many scholars have achieved a series of research findings in the fields of mechanism, the conceptual model and numerical simulation methods of coupled stress-seepage process in recent years. But there are still many unsolved problems, and it's still a key problem all over the world. The most popular used model and mechanism of coupled stress-seepage process in rock are based on some empirical formulas, of which the mechanical concept and parameters are not very clear, and the accuracies are not satisfied.Based on the theories and methods of micromechanics, and from the basic variations of microcracks under mechanical load, the rules of micro stress and deformation of microcracks in brittle rock are studied in mesoscopic view, and a constitutive model of anisotropic damage and a constitutive model of coupled damage and seepage of brittle rock based on micromechanics are built by virtue of homogenization method. Then the constitutive models are verified by the conventional triaxial compression test and seepage test during stress-strain process. In this dissertation, the main investigation work focuses on the following several aspects.(1) The research developments of many fields on the coupling problem of stress and seepage in rock are summarized systematically, which includes the sub-problems such as the mechanism, the conceptual model and the numerical simulation method of the coupling problem of stress and seepage in rock. Some weaknesses of the research are indicated. And also the investigation statuses of micro rock damage mechanics are summarized. On the basis of the above summary and analysis the research emphasis and study methods of this dissertation are presented.(2) Based on the theories and methods of micromechanics, firstly basic assumptions of micro damage constitutive model of brittle rock including microcracks and macro-micro conceptual model are established, and also relation between discontinuous displacement gap of microcracks and local stress field in microscopic view is built. Though the energy principles, the expression of macroscopic free complementary energy of micro cracked rock is deduced. The microcracks under load are divided into two groups according to the open or closed status. The criterion and evolution equation of frictional slip and expanding of the two groups of microcracks under stress increment are investigated. The fourth order tensor of equivalent homogeneous flexibility (or tangent flexibility) of rock which includes a single group of open microcracks or closed microcracks is deduced based on the energy principle. A macroscopic anisotropic damage constitutive model of brittle rock based on micromechanics is established, using the technology of 33 integration directions for the unit surface integration. Physical meanings of parameters in the model are analyzed, and the related computer program is designed to do the numerical simulation with the model. Sensitivity analysis of some main parameters in this model is finished.(3) Some basic assumptions and the conceptual model of seepage process in...