Research On The Rheological Process Of Fractured Granite Under Thermo-Hydro-Mechanical Conditions In Excavation Disturbed Zone And Its Cellular Automata Simulation

With the construction of hydraulic tunnels, highway tunnels, nuclear waste repositories and the development of energy reserves and resource exploitation in deep underground, the long-term stability of deep engineerings is a challenge due to the special circumstances of surrounding rockmass, such as high geostress, high geotemperature, high hydraulic pressure and so on, which result in great changes of mechanic properties of the surrounding rockmass and increasing engineering disasters. Therefore, it is necessary to research the rheological behavior of rockmass in complicated circumstances, which can enrich the content of engineering mechanics and contribute to real rock engineering. On the background of the international DECOVALEX- THMC(Task B) project, Herein the basic problem concerning the rheological behavior of fractured rock mass under thermo-hydro-mechanical(THM) conditions is concerned. Concretely, THM rheological behavior of fractured granite in excavation disturbed zone(EDZ) is simulated by cellular automata with separating into THM rheological analysis of the intact rock and structural plane. The studying mainly covers the following aspects:1. Based on the relation of the creep equations in 1-Dimension and 3-Dimension, two methods to determinate 3-Dimensional(3-D) viscoelastic model parameters are presented. Then the expressions describing the relation between the 3-D parameters and 1-D parameters of generalized Kelvin model are established on the basis of the methods. In addition, for the creep compliance of the generalized Maxwell model is expressed implicitly by the model parameters, in terms of the above methods, a new way to determinate the 3-D parameters of generalized Maxwell model is suggested and verified by the establishment of the expressions describing the relation between the 3-D parameters and 1-D parameters of Poynting-Thmson model.2. It's difficult to obtain the creep compliance of the generalized Maxwell model and Wiechert model due to their parallel connecting structure, but their detailed expressions are presented by Laplace transform and the definition of creep compliance, and the equivalence of the generalized Maxwell model and the Kelvin chain is achieved and the conversion relations of both model's parameters are also derived. Moreover, a inherent property of generalized viscoelastic model obtained is the practical criterion when the rheological behavior of certain material is described by the kind of generalized viscoelastic model. The method to solve the creep compliance of the generalized Maxwell model and the inherent property of generalized viscoelastic model are proved by a couple of examples.3. By using governing equations that describe the fully coupled THM behavior of the rheological porous media, a simplified model of intact granite is brought out according to the features of DECOVALEX-THMC(Task B) project and the creep tests of granite under THM conditions on literature. A plane strain creep joint model is derived under THM conditions on the basis of limit concept, and the equations to consider the effect of temperature and water pressure are also presented. When the creep joint model is applied to the structural plane in numerical simulation, five basic modes of deformation occur. A Goodman joint element with thickness considering the five deformation modes is presented. Due to the special shape of the Goodman joint element, almost all of the relations of mechanical parameters are derived in the global and local coordinates in light of the invariability of tensor, and it can be proved that the coordinate transform expression of the stiffness matrix of Goodman joint element with or without thickness is the similar with that of the thin-layer element introduced by Sharma and Desai.4. According to the cellular automata(CA) theory and rheological theory, CA creep models such as elastic-viscoplastic model, elastic-viscoelastic-viscoplastic model and so forth, are built to solve the rheological problem. Then the VEPCA program developed in Visial C++ environment is to simulate the rheological behavior of fractured rock mass under THM conditions using rheological models of the intact granite and structural plane. Several examples have shown the reliability and rightness of the VEPCA program.Finally, the VEPCA program is used to perform BMT (Benchmark test) simulation of THM processes in DECOVALEX-THMC(Task B) project. Detailed analyses of distribution and evolution of stresses and displacements in WB(Wall-Block) model are discussed during the whole history including the excavation, the pre-emplacement and post closure until the 1 million years. The analysis of WB model is divided into two parts: one is elastic analysis, the other is rheological analysis. Using the GJE1 joint element and GJE2 joint element, respectively, the elastic results are presented and compared in the problem of interpenetration and the problem of open with tensile stress. The clauses and the methods to solve these problems are also discussed. Using the GJE3 joint element which is based on the GJE2 joint element, the rheological results of WB are presented to evaluate the long-term stability of EDZ in underground disposal system.