Rock Blocks In The Rock Arround The Underground Powerhouse Of Three-Gorges Project

The stability of rock blocks is one of the key issues in the underground powerhouse in the Three Gorges Project. The rock mass around the dam site of the Three Gorges project is a hard igneous rock. It is usually believed that the rock mass is of high level of strength and total stability. But the local stability of the rock mass has always been concerned.This dissertation is based on the theory of general block method. Under the engineering background of the underground powerhouse excavated in right bank of the Three Gorges Project, a 3D block model is established by GeneralBlock program in order to identify and analyze the associated stability problem of rock blocks in the vault of caverns and slope of tail water channel. According to the modeling results and combination of different types of rock blocks, design and construction of effective reinforcement are put into practice. In addition, systematic monitorings for bolts, cables and blocks are set up. The monitoring results show that the deformation of block is less than 2 mm, and the stress of anchor bar and loss rate of cable remain stable. These outcomes indicate generally an effective reinforcement.This dissertation systematically analyzed the blockiness of the surrounding rock mass of the underground powerhouse in the Three Gorges Project to quantify its level of being an assemblage of isolated block. Based on measurements of fractures obtained from the field survey, the discrete fracture network model is established by an inverse method for identifying and analyzing rock blocks. The results show that the blockniess of the surrounding rock mass of the underground powerhouse is only 4‰; the quality and the stability of the total rock mass is very well; the number of blocks in the rock mass is quite small; therefore, the volume of isolated blocks only accounts for a very small proportion in the total rock volume; it can be considered as a continuum. The excavation process of the underground powerhouse in the Three Gorges Project verified the conclusions aboved; there is only a few of blocks formed by the fractures in the rock mass of the underground powerhouse. According to ISRM, there are thirty-five kinds of rock mass structural models are established by considering the classification in the fracture. For each of the 35 structures, rock blocks are identified using GeneralBlock program. 5 random realizations are carried out in a specific range of model to reduce the influence of randomness. Thus, through investigation the fluctuation of blockiness with the variance of the scale of model region, the blockiness of each structure and the size of representative elementary volume (REV) can be calculated. The results show that the size of REV of fractured rock mass is between 4 and 12 times of the fracture spacing; for all of the 35 structures, none of these exceeds 12 times of the fracture spacing.The calculation results from the 35 models show that the blockiness of rock mass in medium persistence and very wide spacing is very low. The structure of the surrounding rock mass of the underground powerhouse in the Three Gorges Project belongs to this kind. The blockiness of it is in accord with the result of model calculation. Therefore the calculation results from the 35 models is useful to predict the stability of rock masses in different persistence and spacing, and could provide a reference for quantification the quality of rock masses in other different projects.