Parameter Inverse Problem For Flow Analysis And Flow-Stress Coupled Analysis In Fractured-Rock Masses

Research advances in the fields of seepage parameter inverse problems are reviewed in the paper. Thorough comments are developed on different parameter identification methods as well as suggestions are given about future studies. On the basis of a united mixed media model including porous medium, equivalent continuum fracture medium and discrete fracture medium, the seepage parameter inverse problem about fracture rock masses is studied systematically and some effective measures are presented to decrease the ill-posed property and improve the reliability of parameter identification. The indirect method widely used in parameter identification fields is applied to solve the seepage parameter inverse problem. In order to get the derivatives for water heads against seepage parameters, a new algorithm named direct differentiation algorithm is presented for FEM analysis of seepage problem in fracture rock masses; Based on the new algorithm, a new weight function for the objective function is developed. With the application of the weight function, the effects of monitored water heads with high sensitivity against objective parameters can be strengthen to decrease the ill-posed property of the inverse problem. At the same time, the monitored water heads with low sensitivity are used properly to insure enough monitored information against distortion of the back analysis result. By applying the direct differentiation algorithm based on FEM , Gauss-Newton-Marquit method is also improved in the paper. As a result, several defects due to the difference method in calculating the gradient vector of the objective function are eliminated and the efficiency of Gauss-Newton-Marquit method is raised greatly. Primary genetic algorithm is improved by the construction of individual self-adapting cross and mutation probabilities, and a new hybrid genetic algorithm with high efficiency is presented to decrease several limitations of primary genetic algorithm in practice, such as poor local search ability, premature convergent, excessive computational cost and bad adaptability to large search space. Universal computer code programs are developed separately by combining the above two optimization methods with FEM of seepage problem in fractured rock masses and applied successfully to the seepage parameter back analysis in the foundation of a typical gravitation dam. Because of strong inter action between the fluid flow and stress in fracture rock masses, the parameter inverse problem for the coupled analysis is further studied in which both water heads and displacements are regarded as monitored in formations. The four-freedom complete couple method is used to solve the flow-stress coupled forward problem. In the back analysis of the couple problem, the sensitivity analysis of displacements against mechanical parameters is made firstly, and on the basis of the sensitivity analysis, the objective mechanical parameters are determined. Then the hybrid genetic algorithm is applied to solve the parameter inverse problem. Furthermore, since seepage in deformable fracture rock masses is a dynamic process with strong flow-stress coupling effects,the corresponding numerical analysis should reflect the dynamic characteristics. Therefore, a FEM analysis for the dynamic flow-stress coupling problem is also developed in the paper based on the general partial differential equations of water flow in the deformable medium. And a new numerical integral algorithm with high precision is put forward to calculate the integral term on the boundaries of free surface in the FEM analysis of unstable seepage problems. At the same time, monitored data in situ can be considered as dynamic serials related to time, and a dynamic back analysis method is tried to determine the seepage and mechanical parameters in FEM analysis of the dynamic couple problem. On the basis of the above theories, universal computer codes are developed separately to deal with the static and dynamic parameter inverse problem. And a typical fractured rock slope case study is carr...