Study On Dynamic Feed-Back Optimization Design Method Of Large Underground Powerhouse Cavern Group During Construction Period

Along with the construction of a plenty of large scale hydropower stations, underground powerhouse cavern group, as important hydraulic structure, will be much more difficult to be constructed, compared with general underground engineering. Especially, engineering accidents caused by instability of surrounding rock is quite common. Naturally, stability analysis and control of large underground powerhouse cavern group become problems demanding prompt solution. Hence, centering on this topic, study of dynamic feed-back optimization design method of large underground powerhouse cavern group during construction is carried out in the dissertation, with the purpose of meeting the demand of major hydropower station. A scientific and practical flowchart of dynamic feed-back optimization design during construction is founded, which includes 3 important components:dynamic back analysis of parameters, recognition of failure mode of surrounding rock and dynamic controlling method, and general stability evaluation of powerhouse during stage excavation. Correlative methods and technologies are empathically studied or summarized. Also, all these achievements are successfully used in the construction of Jinpingâ…¡hydropower station.In sum, the main research work and conclusions are as follows:1. Absorbing the advantages of existing dynamic design methods for underground engineering, and according to the characteristics of underground cavern group, a real-time, dynamic and closed loop feed-back optimization design flowchart for large underground powerhouse cavern group during construction is founded, which integrates the development of latest theory and technologies, such as rock mechanics theory and numerical calculation methods, supporting technologies, monitoring and testing methods of surrounding rock, theories and methods of feed-back analysis, system science and engineering optimizing methods, and so on.2. Combined with the widely used intelligent optimization back analysis method, correlative principles, methods and technologies of dynamic back analysis for underground powerhouse during stage excavation are systematically studied, including principles and key points of monitoring design, principles for selecting monitoring data and calculated value, extracting format of calculated variables, back analysis technologies for three-dimensional calculation, and so on. With the research, the reliability and efficiency of back analysis result is ensured. 3. According to tests of integrated samples and samples with structural plane in different lithology under stress paths which simulate the excavation and supporting process of underground engineering, and summarization of existing research results about stability analysis and control for underground engineering, local failure problem of surrounding rock for large underground powerhouse cavern group is deeply, systematically and multi-angle studied for the first time at home and abroad, including classification of failure mode, failure mechanism, occurrence condition of failure, general occurrence parts, analysis methods and controlling measures. Also, a dynamic controlling method for local failure of surrounding rock during construction is presented. The research production is an important link of dynamic design method and distinguishing feature for practicability, to which the researchers and designers on site can conveniently refer in all directions.4. As the equivalent rock mechanical parameters obtained by intelligent optimization back analysis synthetically reflect the changes of geological conditions, various monitoring and testing information, and the process of excavation and supporting, fuzzy comprehensive evaluation is used to conduct integral stability apprise of underground powerhouse based on the result of dynamic back analysis. It is to be noted that this method synthetically considers rock deterioration, failure mechanism and influence of various uncertain factors during construction, and can be taken as seientific basis for optimization design.5. The dynamic feed-back optimization design method proposed in this paper is successfully used in the powerhouse cavern group construction of Jinpingâ…¡hydropower station and the third excavation stage is taken as a example to show the usage of the flowchart. Research results summarization of the whole excavation process indicates that the method is not only practical and workable, but also adequate to seize the mechanical behavior of surrounding rock during excavation, which is worthy of reference for other engineering of this kind.