Theory And Practice On The Feedback Simulation Analysis Of Geotechnical Structure

Geotechnical engineering is a frontier science of civil engineering and geology, it is established on the basis of the knowledge combined organically by soil mechanics and foundation engineering and rock mechanics to probe and solve the technology problems about rock and soil engineering. As a result of the complicity and uncertainty of the material and the complicated geotechnical structures and many influenced factors, geotechnical engineering is a very complicated subject of popular concerns. With the development of the Chinese economy, more and more geotechnical technology problems in the construction of hydroelectric projects and traffic projects and ocean exploitation projects and mining projects are presented on the face of the engineers.Since 1960's, with the development and popularization of the computer technology, numerical modeling method of geotechnical engineering advances rapidly. The practice indicates that the stresses and the deformation and the breakage analysis can be obtained by the numerical method in the field of the ground engineering, underground engineering, slope engineering and dam engineering etc. And the achievements can also be applied into the designs. The qualitative analysis transits to the quantitative analysis as the progress of the geotechnical numerical method. The most important factors influenced on the reliability of the calculated results are the accuracy of the mechanics parameter and the description of the constitutive model for the geotechnical materials, and the in situ stresses field. So the inaccuracy of the mechanics parameter and the difficulty of confirming the constitutive equations have been the bottleneck problem for the theory analysis and numerical modeling in the geomechanics.Therefore, this thesis is focused on the key geotechnical technique problems in several large hydroelectric projects in China, the feedback simulation analysis of geotechnical structures, and some important practical conclusions and realizations are presented. Finally, the feedback simulation analysis system with a plenty of functions is successfully developed, and applied to solve the practical problems in a few important large projects perfectly.This thesis includes nine chapters. The detail are listed as follow:Chapter one summarizes the development and the state-of-art of the numerical modeling methods and back analysis methods for geotechnical structures, several questions of thefeedback simulation analysis in geotechnical structures are pointed out. Based on these questions, the research work and the signification of this thesis are determined.Chapter two discusses the general mechanics models which include the nonlinear elasticity, and the perfectly elsto-plasticity, and the elsto-visco-plasticity and the Cam-Clay constitutive models for geotechnical structures, and also include the model of the joint surface and the anchor measures. According to the characteristic and the mechanism of the reinforcements in joint rock, the mechanics model for the bolted joint rock is studied deeply. This model can be applied to study the deformation and the stresses of the local key position by the dispersing model of the faults and the cracks and the anchor bars, and can also be used to analysis macroscopically the influences of the unsubstantial constitution by the equivalent method. This model is distinctly better than the traditional mechanics models.Chapter three is concentrated on studying the general finite element method on the basis of the control equations of the geotechnical engineering, and the common nonlinear analysis method which are the nonlinear elasticity analysis and the elasto-plasticity analysis and the elasto-visco-plasticity analysis, and the modeling method of excavating and backfilling process are studied thoroughly.It is a perfect idea that the dense mesh should be matching with the stress concentration part and the large size mesh could be adopted for the less stress grads during the finite element calculating. However, it is very difficult to estimate exactly the stresses distribution in advance for the complicated structures. The adaptive finite element method is the one better approach of solving this problem. At present, the adaptive finite element method includes h- type > />-type% r-type, h-p type, and the A-type adaptive finite element theory is recommended in this chapter.According to the selection of the time step length for the saturation soil, the length is neither too large nor too small. The too large time step length will result in large error, and the too small time step length will increase the computing work. For the dynamic analysis, the same problem also exists. And then, based on the BIOT consolidation theory and the dynamical control equations and the error estimation theory, the adaptive equations of time step length for the consolidation analysis and dynamic analysis are established and the result provide a effective approach for the selection of the time step length.Chapter four is focused on studying the methodology of the feedback analysis ofgeotechnical engineering, the artificial neural network (ANN) back analysis method and the genetic algorithm (GA) back analysis method are presented on the basis of the nonlinear finite element analysis method. The applicability and the deficient parts of ANN back analysis and GA back analysis are discussed, and then the improved scheme is presented, the practical combined back analysis model of GA-ANN is established.ANN has the strong capability of study and memory and nonlinear expression, especially it is fit for the description of the nonlinear relationship between the mechanics parameter and the constitutive model for rock and soil material with the deformation. Compared with ANN, the main advantage of GA is the full optimization, and the disadvantage of GA is the slow convergence. Considered the strong points of both GA with ANN, the combination back analysis model built in this chapter can improve the convergence velocity and the full searchingChapter five introduces the specialties and the functions of the feedback simulation analysis system of geotechnical structures developed by this thesis, and the organization of this system, and a few typical examples are cited to verifying the program.Chapter six to chapter eight are the application research on the practical engineering. The simulation feedback analysis system is applied into studying the stability and the deformation of the intake slope in Longtan hydraulic project and the stability of the rock filled dam and the seepage prevention system in Pubugou and the in situ stresses field of Pubugou underground caverns.In chapter six, according to monitored data of 1-1 and 2-2 section of the intake rock slope located in the left bank of Longtan hydraulic project during the constructing process, the mechanics parameter of the rock are obtained by the simulation feedback analysis system, and then the real-time tracing prediction and the optimization of the engineering measures are achieved. Finally this chapter gives out some references for the decision-making of the designers and the constructers.Chapter seven applies the back analysis system to establish the in situ stresses field of the Pubugou underground plant zone, the achievements are very consistent with the actual cases and can taken as the basis data for the further study.Chapter eight adopts the adaptive finite element method into studying the stability and the deformation of the Pubugou rock filled dam. Especially, the type selection of jointbetween the concrete cutoff wall and the core clay wall is deeply studied, and the rational type joint is presented for the designers.Chapter nine summarizes the research works and the results. At last, the author gives some point views and the prospects of the further study on the feedback simulation analysis of geotechnical engineering.