Study On Surrounding Rock Stability Of Deep-lying Diversion Tunnel In Jingping Cascade 2 Hydropower Station.

Currently, with the continued and fast development of our nation economy, some new chances are met in the development of hydroelectricity construction. At the same time, a large number of new projects are put forward. The four diversion tunnels of Jinping Cascade 2 Hydropower Station is about 18 km long and 2500m deep in maximal bury-depth, which are the longest and deepest diversion tunnels in the world. Because these tunnels have great depth, quiet length, abundant ground water and complex geological conditions, a series of special geological problems will be met in the process of design and construction, for example high geo-stress, high external water-pressure, high water-gushing and rock-burst, and so on. The analysis and study of surrounding rock stability is very necessary, which relates to our life and property security. How to evaluate surrounding rock stability is a hot problem in the world of engineering and science.This paper sticks to the evaluation of surrounding rock stability of deep-lying tunnel in order to direct tunnel's design and construction in Jinping Cascade 2 Hydropower Station project, and studied surrounding rock stability of tunnel systematically. Therefore, this paper mainly has done the following work:Primarily, some main elements influencing the surrounding rock stability were discussed. Next, this paper analyzed the failure forms and mechanics of surrounding rock stability, based on which mechanical state was discussed in the course of excavation. Finally, several collapsing criterions were analyzed.Next, main engineering geological conditions and problems of diversion tunnel zone were analyzed.with the development of artificial neural network and fuzzy theory, by which a surrounding rock classification estimate system(Adaptive Network-based Fuzzy Inference System) was developed on the basis of conventional method, which open a new way to determination surrounding rock classification.Based on the large analysis software FLAC^3D, this paper built the numerical simulation model with the effects of high geo-stress, high external water-pressure, analyzed the stress distribution, deformation and plastic range of the surrounding rock in the process of excavation and support of the tunnel. Firstly, this paper discussed the influences on the stress, deformation and plastic range, because of the unloading of excavation. Secondly, to reflect the character of the tunnel's design and construction, this paper compared the different construction step (full-face and up-down excavation). On the basis of the unloading of excavation and stress relieving of surrounding rock, different supporting- moment were discussed, consequently, the...