| This thesis will be the part research report of the Interaction between the chamber wall structure and the slope of the permanent rock in Three Gorges project. The local stability problems for the rock blocks with different sizes were presented in the excavation process of the rock foundation of the permanent lock. The elastic rock mass and the elastic chamber wall were used in the previous studies under the assumption of the stable rock mass. The question such as the stability of the local rock block and their influence to the chamber wall can't be answered from those researches since the nonlinear properties of rock mass were not simulated. The interaction among the camber wall, anchorage bars, anchorage cables, rock mass and the key rock block is studied in this thesis. The full concrete pouring process and its temperature action are all simulated. The nonlinear properties of the weak surface and the contacting mechanism between the chamber wall and the rock mass are considered in the analysis. The stability of the rock block is finally given by using the nonlinear FEM and limit balance theory for the rigid body. The results will provide the theory basis for the permanent lock design.The following are the new points in this thesis:1. Time discretion for the finite element analysis of the unsteady temperature field and the automatic generation of the heat releasing boundaries1.1 Instead of the difference method, which is usually used for the time discretion of the temperature variable when the finite element is used, the Taylor expansion method is used in this thesis. It will make the equations for the temperature field compatible with the used program. Moreover, the unified equations are obtained for both of implicit and explicit algorithm of the temperature field.1.2 The heat releasing boundaries are updated in the concrete pouring process time to time. It is difficult to find the heat releasing boundaries corresponding to a given construction time by hands. An automatic generation method of the heat releasing boundaries is presented in this thesis.2. Study of FEM for the rock mass with the weak layer and the friction contact problems with initial gaps2.1 The accuracy by using the rectangle or the column element to describe the plane or the space rock mass problems with the weak thin layer is higher than that of the simplified joint element or the thin layer element.2.2 The contact state simulation by using the Gauss points in the rectangle or the column element is presented to solving the friction contact problems with initial gaps. The iterations for the contact state and the iterations for the friction condition under the closed state can be done simultaneously by this method. Moreover, It has the following advantages: (a) the contact problems with the cross intersections or inflection points on the contact surfaces can be solved effectively; (b) the contact joints due to the construction can be easily and accurately simulated.2.3 The reasonable analysis method is presented to solve the weak surface problems with zero thickness. The generalized Mohr-columb yielding criteria is presented for the weak thin layer materials since the yielding and the failure are usually along the strike of the weak surfaces.3. The advantages and the disadvantages of the existing directed and iterative methods for solving finite element equations are concluded. The structural block preconditioned conjugate gradient iterative method is presented to improve the Jacobi preconditioned conjugate gradient iterative method which is widely used in the world. This method is very effective for solving the large linear equations with local material nonlinear problems.4. The kinds of nonlinear problems in structural finite element analysis are concluded and the equations for solving the elastoplastic problems are formulated. The Newmann expansion method for the inverse matrix computation of the stiffness matrix is firstly induced. It makes only renewing the local inverse matrix for local nonlinear problems...
|
PDF Full Text Request