Application Of The Theory Of New Austrian Tunneling Method To Longtan Underground Power House

The scale of the Underground Power House of Longtan Hydropower Station is the world's record at present. With numerous crossing and overlapping tunnels ,thinner rock pillars between tunnels and complicated engineering geological conditions, the underground project poses a high technological difficulty to the project builders. How to solve the problems of the safety and stability of the surrounding rock is a difficult point for the design and construction of Longtan Underground Power House . In facing with such huge and complicated systematic project as Longtan Underground Power House, we urgently need a systematic and effective basic theory to guide the overall course of construction , in order to ensure a good solution for surrounding rock stability in aspect of construction orgnization, technology, procedures, measures and methodology, so as to guarantee a smooth implementation of project.NATM is to apply the fundamental principle of rock mass mechanics, with maintaining and utilizing the self-stable ability as a base point, withanchoring spray as the main protective support means, to monitor the dynamic status of the underground surrounding rock after excavation by surveying and measuring, with which, to guide the design and construction of the protective support structure of the underground engineering. It is a effective methodology and the theory at present extensively applying to the construction of underground projects. According to the engineering practice, to ensure the tunnel surrounding rock stability, we observed the theory of New Austrian Tunneling Method throughout the overall course of longtan underground powerhouse desigrrand construction. The analysis and research work we conducted include the following: in early stage, based on the engineering analogy method and the engineering characteristics, we set up relevant parameters for excavation and protective support, and check them by model test and theoretical calculation; We studied solutions, procedures, methods and control measures for excavation and protective support; The status in which the possibility and the timing of potential unstability and the transformation of surrounding rock due to release of stress will be quickly and accurately analysed and judged based on the surveying and measuring results; the protective support parameters will be evaluated, and the design will be improved through revision. With this way, a dynamic monitoring and informatory designing is realized. All of the above will serve as the bases for design and construction, to ensure safety for construction of the underground power house.