Feedback Analysis Based On Monitoring Of The Caverns Excavation Of Underground Hydropower Plants

In recent years, since the number of hydropower stations with underground plants in China becomes larger, and the size of powerhouse plants gets bigger, the stability problem of surrounding rock mass after construction becomes more important and complex. Some problems of the excavation are difficult to be predicted by engineering experiences because of the complexity of underground rock mass. Therefore numerical methods are needed to solve such problems. With the help of three-dimensional numerical simulation, we can know not only the deformation and stress of cross sections, but also the security and stability of some important spatial regions.The feedback analysis method has been used popularly in hydraulic engineering, particularly in the analysis of stability of the underground engineering, with the development of numerical methods. It is usually used for generating the initial geostress field or choosing the values of rock parameters. But it is rarely used for simulating the whole process of underground engineering, especially in three-dimension numerical simulation, which is more close to the fact of engineering and has more effect on the engineering comparing with two-dimension numerical analysis.This article is committed to the establishment of a complete system of feedback analysis, which can be used in the three-dimension numerical computing of underground engineering. The constitution of the numerical model, the regression of initial geostress field, the selection of rock parameters and result analysis are concluded in this system. It uses a number of commercial software, e.g. Fast Lagrangian Analysis of Continua in three-Dimensions (FLAC3D), MATLAB toolbox of artificial neural network. This system integrates all steps of three-dimension numerical computing used in underground engineering together to form a complete computing routine, which can be applied in other engineering.The accuracy of the numerical result depends on the following factors: the accuracy of numerical model, the accurate simulation of excavation process and support such as the cable, the concrete lined and so on, the generating of the initial geostress field, the values of rock parameters selected in the model, and so on. Of these factors, the initial geostress regression is the foundation and the parameter selection of surrounding rock mass is the emphases. In regard to the initial geostress regression, this paper puts forward a method using two sets of model grids to solve the problem of disordered initial stress exited in caverns regions. Two methods, single parameter and multi-parameter sensitivity analysis, are used for the calculation, comparison, analysis of the sensitivity of rock parameters and finding out the parameter which has more influence on the numerical result.Based on the monitoring data of underground plants of left riverside of the Xiluodu Hydropower Station, in Jinsha River, we analyses the stability of rock mass and forecast what will happen in next construction. The final purpose is to guide the other actual projects.