Study On The Numerical Method For The Seepage And Stress Analysis Of Rock Mass

Faults, joints and fractures are widely distributed in rock masses. These discontinuous surfaces play a regulatory role on the seepage and stress characteristics of rock masses. Accordingly, some numerical simulation methods had been put forward over the past years. To sum up, these methods are based on two categories: continuum mechanics method and non-continuum mechanics method. The Finite Element Method (FEM) and the Finite Difference Method (FDM) are the representatives of continuum mechanics method. The Discrete Element Method (DEM), Block Element Method (BEM) and the Discontinuous Deformation Analysis Method (DDA) are the representatives of non-continuum mechanics method. The newest method such as Numerical Manifold Method (NMM) and Mesh-Free Method (MFM) can simulate both the continuum and non-continuum deformation.The FEM based on continuum mechanics is widely used in the geotechnical engineering. Due to the complex character of the geotechnical engineering, the pre process is a time-consuming and painful job. In this thesis, based on the frame work of finite element method, three kinds of new numerical methods are presented:the discontinuous finite element method for the dam/foundation system, the dynamic finite element method for the excavation simulation, and the improved superposed element method.The non-continuum mechanics can describe the seepage and stress characteristics of rock mass well. In this thesis, based on the Block Element Method, the automatic identification method for three dimensional random fracture network is put forward, then, the seepage, stress and coupling characteristics are studied and discussed.In conclusion, the mainly innovation points of this thesis are as follows:(1) The Discontinuous Finite Element Method (DFEM) for the dam/foundation system is presented. By using this method, the complex domain for the whole system can be divided into two unconcerned domains:the domain of dam and the domain of foundation. The elements connected to the base surface are coupled, using the geometric compatibility equation by the deformation of the dam and foundation connected to the base surface, constitutive equations of the base surface, and the equilibrium equations of the whole system. And the new method is extended into the seepage analysis field for the dam/foundation system too, which can make up as a whole numerical method with the stress analysis method. A gravity dam on complicated foundation is studied, and the results are in accordance with those from the general finite element method, the precision and validity of this method is proved.(2) Refer to the Numerical Manifold Method, the dynamic finite element method for the excavation simulation of complex rock slope is presented. By using this new method, because there is no explicit excavated elements, and only the discontinuous surface and complex terrain should be taken into account, the excavated surface just be inputted as a real-time dynamic parameters, the difficulty of the pre process can be significantly deduced. The excavation simulation of peacock slope of Xiao Wan arch dam is studied, which proves the correctness and effectiveness of the method in the thesis.(3) Base on the main ideas of discontinuous finite element method for the dam/foundation system and the dynamic finite element method for the excavation simulation, a renew Superposed Element Method (SEM) is presented, which can improve the calculative accuracy. Then, the new SEM is extended to three dimension space. Last, the initial gravity field around the underground powerhouse of SeErGu hydropower station is studied with the three dimensional SEM. And the results are in accordance with those from the finite element method, the precision of SEM is proved.(4) Fractures in rock masses are randomly distributed, including the number and size. In this thesis, the Monte Carlo method is adopted to generate the stochastic fracture network first; second, on the base of the theory of directed body, the automatic identification method for three dimensional network with random fractures is realized; thirdly, based on the assumption that the intact rock is impervious and the water flows only along the fractures, the block element method for seepage analysis of three dimensional network with random fractures is established. Finally, two examples are studied to prove the precision and validity of this method.(5) All the faults and joint are all treated as fractures and assumed as "filled medium", which enables to treat the rock fractures with or without fillings coincidently. The relationship between the stiffness coefficient, hydraulic conductivity coefficient and the normal effective stress is deduced. Based on the principle of the block element method, seepage-stress coupling model for three dimensional fracture rock mass is built by using the iterative algorithm. The ShaTuo gravity dam is studied to prove the precision and validity of this method.